One mole of ${\rm{C}}{{\rm{O}}_2}$ contains

3 g atoms of ${\rm{C}}{{\rm{O}}_2}$

$18.1 \times {10^{23}}$ molecules of ${\rm{C}}{{\rm{O}}_2}$

$6.02 \times {10^{23}}$ atoms of O

SOME BASIC CONCEPTS OF CHEMISTRY MCQs for NEET UG CHEMISTRY — Mixed difficulty

1 Easy

Understanding +4 | -1

While titrating dilute

HCl

solution with aqueous NaOH, which of the following will not be required?

View answer and explanation

Correct option: C

Bunsen burner and measuring cylinder

Option C is correct because a Bunsen burner and measuring cylinder are not typically required for a simple acid-base titration.

Solution approach

Correct Answer + Core Reason: Bunsen burner and measuring cylinder. These are not needed for a simple acid-base titration.

Step-by-Step Solution:

Step 1: Identify the necessary equipment for acid-base titration.

Step 2: Pipette is used to transfer a known volume of the acid or base.

Step 3: Burette is used to deliver a known volume of the titrant.

Step 4: Porcelain tile is used to observe the color change at the endpoint.

Step 5: Clamp is used to hold the burette.

Step 6: Phenolphthalein is used as an indicator.

Step 7: Bunsen burner and measuring cylinder are not required for this titration.

Step 8: Final Answer: Bunsen burner and measuring cylinder.

Why other options are wrong:
- Option A: Pipette and distilled water are essential for preparing and diluting solutions.
- Option B: Burette and porcelain tile are essential for performing the titration and observing the endpoint.
- Option D: Clamp and phenolphthalein are essential for holding the burette and indicating the endpoint.

Key Concepts:
- Acid-base titration
- Titration equipment

Memory Aids:
- Remember the purpose of each piece of equipment in a titration.

Quick Tips:
- Understand the procedure for acid-base titration.

2 Easy

2 of 302Question permalink

Application +4 | -1

Which has the maximum number of molecules among the following

View answer and explanation

Correct option: C

8\,g\,\,{H_2}

Option C (

8\,g\,\,{H_2}

) is correct because it has the highest number of moles, and therefore the largest number of molecules.

Solution approach

Correct Answer + Core Reason: $8\,g\,\,{H_2}$ . This contains the maximum number of molecules because it has the highest number of moles.

Step-by-Step Solution:

Step 1: Calculate the number of moles for each option using the formula: moles = mass / molar mass.
- A: $44g\,\,C{O_2}$ : Molar mass of $CO_2$ = 44 g/mol. Moles = 44/44 = 1 mol
- B: $48g\,\,{O_3}$ : Molar mass of $O_3$ = 48 g/mol. Moles = 48/48 = 1 mol
- C: $8\,g\,\,{H_2}$ : Molar mass of $H_2$ = 2 g/mol. Moles = 8/2 = 4 mol
- D: $64g\,\,S{O_2}$ : Molar mass of $SO_2$ = 64 g/mol. Moles = 64/64 = 1 mol

Step 2: Compare the number of moles. The largest number of moles is in option C.

Step 3: Conclusion: Option C contains the maximum number of molecules.

Why other options are wrong:
- Option A: The number of moles of carbon dioxide is less than that of hydrogen.
- Option B: The number of moles of ozone is less than that of hydrogen.
- Option D: The number of moles of sulfur dioxide is less than that of hydrogen.

Key Concepts:
- Mole concept
- Molar mass
- Avogadro's number

Memory Aids:
- moles = mass / molar mass

Quick Tips:
- Always convert mass to moles before comparing the number of molecules.

3 Medium

3 of 302Question permalink

Understanding +4 | -1

One mole of

\mathrm{C}{\mathrm{O}_2}

contains

View answer and explanation

Correct option: D

6.02 \times {10^{23}}

atoms of C

The correct answer is D (

6.02 \times {10^{23}}

atoms of C) because one mole of any substance contains Avogadro's number of entities, and in one mole of

CO_2

there is one mole of carbon atoms.

Solution approach

Correct Answer + Core Reason: $6.02 \times {10^{23}}$ atoms of C. One mole of any substance contains Avogadro's number of entities.

Step-by-Step Solution:

Step 1: Define the mole concept: One mole of any substance contains Avogadro's number ( $6.022 \times 10^{23}$ ) of entities (atoms, molecules, ions, etc.).

Step 2: One mole of $CO_2$ contains one mole of carbon atoms and two moles of oxygen atoms.

Step 3: Therefore, one mole of $CO_2$ contains $6.022 \times 10^{23}$ carbon atoms.

Why other options are wrong:
- Option A: 3 g atoms of $CO_2$ is incorrect. A gram atom is another term for a mole of atoms. There are 1 mole of C and 2 moles of O, totaling 3 moles of atoms, but not 3 moles of $CO_2$ .
- Option B: $18.1 \times {10^{23}}$ molecules of $CO_2$ is incorrect. One mole of $CO_2$ contains $6.022 \times 10^{23}$ molecules of $CO_2$ .
- Option C: $6.02 \times {10^{23}}$ atoms of O is incorrect. One mole of $CO_2$ contains $2 \times 6.022 \times 10^{23}$ oxygen atoms.

Key Concepts:
- Mole concept
- Avogadro's number

Memory Aids:
- One mole = $6.022 \times 10^{23}$ entities.

Quick Tips:
- Remember Avogadro's number and its significance.

4 Medium

4 of 302Question permalink

Understanding +4 | -1

The number of molecules present in 1 mL of gas or vapour at STP is:

View answer and explanation

Correct option: C

Both (1) and (2)

Option C (Both (1) and (2)) is correct because the number of molecules present in 1 mL of gas or vapor at STP is called Loschmidt's number and is equal to approximately 2.687 × 10¹⁹ per mL.

Solution approach

Correct Answer + Core Reason: Both (1) and (2). Loschmidt's number is the number of molecules in 1 mL of an ideal gas at STP, which is approximately 2.687 × 10¹⁹.

Step-by-Step Solution:

Step 1: Recall the definition of Loschmidt's number.\nLoschmidt's number is defined as the number of molecules in 1 mL of an ideal gas at standard temperature and pressure (STP).

Step 2: Recall the value of Loschmidt's number.\nThe value of Loschmidt's number is approximately $2.687 \times 10^{19}$ molecules per mL. The value given in the option is $2.617 \times 10^{19}$ which is close enough to be considered correct.

Step 3: Combine the results.\nSince both statements are correct, the answer is Both (1) and (2).

Why other options are wrong:
- Option A: This option is incomplete because it only states that it is called Loschmidt's number but doesn't include the numerical value.
- Option B: This option is incomplete because it only states the numerical value but doesn't mention Loschmidt's number.
- Option D: Since both statements are correct, this option is incorrect.

Key Concepts:
- Loschmidt's number
- Standard Temperature and Pressure (STP)

Memory Aids:
- Remember the definition of Loschmidt's number as the number of molecules in 1 mL of an ideal gas at STP.

Quick Tips:
- Be familiar with the definition and approximate value of Loschmidt's number.

5 Easy

5 of 302Question permalink

Remembering +4 | -1

The significant figures in 3400 are

View answer and explanation

Correct option: A

2

Option A (2) is correct because only the '3' and '4' are significant; trailing zeros without a decimal point are ambiguous.

Solution approach

Correct Answer + Core Reason: 2. Significant figures are the digits that carry meaning contributing to its measurement resolution.

Step-by-Step Solution:

Step 1: Identify the number: 3400

Step 2: Apply the rules for significant figures:
- All non-zero digits are significant.
- Zeros between non-zero digits are significant.
- Leading zeros are not significant.
- Trailing zeros are significant only if the number contains a decimal point.

Step 3: In 3400, the digits 3 and 4 are significant. The two trailing zeros are not significant because there is no decimal point.

Step 4: Therefore, the number of significant figures is 2.

Why other options are wrong:
- Option B: 5 is incorrect. There are only two significant figures.
- Option C: 6 is incorrect. There are only two significant figures.
- Option D: 4 is incorrect. There are only two significant figures.

Key Concepts:
- Significant Figures
- Rules for Significant Figures

Memory Aids:
- Remember the Pacific-Atlantic rule: If the decimal point is present (Pacific side), start counting significant figures from the left, starting with the first non-zero digit. If the decimal point is absent (Atlantic side), start counting from the right, starting with the first non-zero digit.

Quick Tips:
- Pay close attention to the presence or absence of a decimal point when determining significant figures.

6 Medium

6 of 302Question permalink

Analyzing +4 | -1

Statement I: Equimolar solutions of

\mathrm{H}_3 \mathrm{PO}_3

and

\mathrm{H}_2 \mathrm{SO}_4

are not equinormal.

Statement II: Both are dibasic acid and Molarity

\times 2=

normality.

View answer and explanation

Correct option: D

Statement I is false; Statement II is true

Option D (Statement I is false; Statement II is true) is correct because H3PO3 is a dibasic acid while H2SO4 is also a dibasic acid, therefore equimolar solutions will not be equinormal.

Solution approach

Correct Answer + Core Reason: Statement I is false; Statement II is true. H3PO3 is dibasic, H2SO4 is dibasic, so equimolar solutions are equinormal.

Step-by-Step Solution:

Step 1: Analyze Statement I: Equimolar solutions of H3PO3 and H2SO4 are not equinormal.\nH3PO3 (phosphorous acid) is a dibasic acid because it has two ionizable hydrogen atoms. H2SO4 (sulfuric acid) is a dibasic acid because it has two ionizable hydrogen atoms. Since both acids are dibasic, equimolar solutions of both acids will have the same normality (Normality = Molarity × Basicity). Therefore, Statement I is false.

Step 2: Analyze Statement II: Both are dibasic acid and Molarity × 2 = normality.\nThis statement is true. Both H3PO3 and H2SO4 are dibasic acids, meaning they can donate two protons (H+) per molecule. For dibasic acids, Normality = Molarity × 2.

Why other options are wrong:
- Option A (Statement I is true; Statement II is true; Statement II is the correct explanation of Statement I): Statement I is false.
- Option B (Statement I is true; Statement II is true Statement II is not the correct explanation of Statement I): Statement I is false.
- Option C (Statement I is true; Statement II is false): Statement I is false.

Key Concepts:
- Basicity of Acids
- Molarity
- Normality

Memory Aids:
- Normality = Molarity × n-factor (where n-factor is the number of replaceable H+ ions in an acid or OH- ions in a base).

Quick Tips:
- Remember that H3PO3 is dibasic, not tribasic. The structure of H3PO3 has only two P-OH bonds, and one direct P-H bond, which is not ionizable.

7 Medium

7 of 302Question permalink

Application +4 | -1

In the equation,

\mathrm{SnC}{\mathrm{l}_2} + 2\mathrm{HgC}{\mathrm{l}_2} \to \mathrm{H}{\mathrm{g}_2}\mathrm{C}{\mathrm{l}_2} + \mathrm{SnC}{\mathrm{l}_4}.

. The equivalent weight of stannous chloride (molecular weight = 190) will be :

View answer and explanation

Correct option: B

95

Option B (95) is correct because the equivalent weight is calculated by dividing the molecular weight by the change in oxidation state, which is 2 in this case.

Solution approach

Correct Answer + Core Reason: 95. The equivalent weight is the molecular weight divided by the change in oxidation state.

Step-by-Step Solution:

Step 1: Identify the change in oxidation state of Sn in the reaction.\nSnCl2 -> SnCl4. The oxidation state of Sn changes from +2 to +4.

Step 2: The change in oxidation state is 4 - 2 = 2.

Step 3: Calculate the equivalent weight: Equivalent weight = $\frac{{\text{{Molecular weight}}}}{{\text{{Change in oxidation state}}}} = \frac{{190}}{2} = 95$

Step 4: Final Answer: 95

Why other options are wrong:
- Option A: 190: This is incorrect because it is the molecular weight, not the equivalent weight.
- Option C: 47.5: This is incorrect. It would be the equivalent weight if the change in oxidation state was 4.
- Option D: 154.5: This is an incorrect calculation and doesn't relate to the correct method.

Key Concepts:
- Equivalent weight
- Oxidation state
- Redox reactions

Memory Aids:
- Equivalent weight = (Molecular weight) / (n-factor)

Quick Tips:
- Determine the change in oxidation state carefully.

8 Hard

8 of 302Question permalink

Application +4 | -1

The number of

C{l^ - }

ions in 100 ml of 0.001M HCl solution is

View answer and explanation

Correct option: C

6.022 \times {10^{19}}

Option C (

6.022 \times {10^{19}}

) is correct because the number of chloride ions is calculated from the molarity and volume of the HCl solution.

Solution approach

Correct Answer + Core Reason: $6.022 \times {10^{19}}$ . The number of ions is calculated using molarity, volume, and Avogadro's number.

Step-by-Step Solution:

Step 1: Calculate the number of moles of HCl: Moles = Molarity x Volume (in L) = $0.001 \text{ M} \times 0.1 \text{ L} = 0.0001 \text{ moles}$

Step 2: Since HCl is a strong acid, it completely dissociates into $H^+$ and $Cl^-$ ions. Therefore, the number of moles of $Cl^-$ ions is equal to the number of moles of HCl.

Step 3: Calculate the number of $Cl^-$ ions: Number of ions = Moles x Avogadro's number = $0.0001 \times 6.022 \times 10^{23} = 6.022 \times 10^{19}$

Why other options are wrong:
- Option A: This is incorrect because it uses the Avogadro's number directly without considering the number of moles.
- Option B: This is incorrect because of a calculation error in determining the number of ions.
- Option D: This is incorrect because of a calculation error in determining the number of ions.

Key Concepts:
- Molarity
- Avogadro's number
- Dissociation of strong acids

Memory Aids:
- Molarity = Moles / Volume
- Avogadro's number = $6.022 \times 10^{23}$

Quick Tips:
- Remember to convert volume to liters before calculation.

9 Medium

9 of 302Question permalink

Analyzing +4 | -1

Which of the following contains greatest number of oxygen atoms?

View answer and explanation

Correct option: D

All have the same number of atoms

Option D (All have the same number of atoms) is correct because 1 g of any element will have the same number of atoms if we're considering individual atoms of oxygen.

Solution approach

Correct Answer + Core Reason: All have the same number of atoms. The question asks for the number of oxygen *atoms*, not molecules.

Step-by-Step Solution:

Step 1: Understand the question. We need to determine which option contains the greatest number of individual oxygen atoms.

Step 2: Analyze each option:
- Option A: 1 g of O contains a certain number of O atoms.
- Option B: 1 g of O $_2$ contains O $_2$ molecules, each with two O atoms. We need to find the mass of O atoms in 1 g of O $_2$ .
- Option C: 1 g of O $_3$ contains O $_3$ molecules, each with three O atoms. We need to find the mass of O atoms in 1 g of O $_3$ .

Step 3: Calculate the mass of O atoms in each option:
- Option A: 1 g of O contains 1 g of O atoms.
- Option B: 1 g of O $_2$ contains (32 g O $_2$ /mole O $_2$ ) and (2 * 16 g O atoms/mole O $_2$ ). So, 1 g O $_2$ contains (1 g O $_2$ ) * (32 g O $_2$ /mole O $_2$ ) $^{-1}$ * (32 g O atoms/mole O $_2$ ) = 1 g of O atoms.
- Option C: 1 g of O $_3$ contains (48 g O $_3$ /mole O $_3$ ) and (3 * 16 g O atoms/mole O $_3$ ). So, 1 g O $_3$ contains (1 g O $_3$ ) * (48 g O $_3$ /mole O $_3$ ) $^{-1}$ * (48 g O atoms/mole O $_3$ ) = 1 g of O atoms.

Step 4: Conclusion: All options contain 1 g of O atoms, therefore, they all have the same number of oxygen atoms.

Why other options are wrong:
- Option A: Incorrect because the other options also contain the same number of oxygen atoms.
- Option B: Incorrect because the other options also contain the same number of oxygen atoms.
- Option C: Incorrect because the other options also contain the same number of oxygen atoms.

Key Concepts:
- Mole concept
- Atomic mass
- Molecular mass

Memory Aids:
- Remember to consider the number of atoms within each molecule.

Quick Tips:
- Always read the question carefully to understand what is being asked (atoms vs. molecules).

10 Medium

10 of 302Question permalink

Application +4 | -1

An ore contains 1.34% of the mineral argentite,

\mathrm{A}{\mathrm{g}_2}\mathrm{S}

, by mass. How many gram of this ore would have to be processed in order to obtain 1.00 g of pure solid silver, Ag?

View answer and explanation

Correct option: B

85.7 g

Option B (85.7 g) is correct because it involves calculating the mass of ore needed based on the percentage of argentite and the stoichiometry of silver in argentite.

Solution approach

Correct Answer + Core Reason: 85.7 g. This is calculated based on the percentage of argentite in the ore and the mass ratio of silver in argentite.

Step-by-Step Solution:

Step 1: Given: Ore contains 1.34% of $\mathrm{A}{\mathrm{g}_2}\mathrm{S}$ by mass. We want to obtain 1.00 g of Ag.

Step 2: Molar mass of $\mathrm{A}{\mathrm{g}_2}\mathrm{S}$ = 2(107.87) + 32.06 = 247.8 g/mol

Step 3: Mass of Ag in 1 mole of $\mathrm{A}{\mathrm{g}_2}\mathrm{S}$ = 2(107.87) = 215.74 g

Step 4: Mass fraction of Ag in $\mathrm{A}{\mathrm{g}_2}\mathrm{S}$ = $\frac{{215.74}}{{247.8}} = 0.8706$

Step 5: Let 'm' be the mass of the ore. Then, 0.0134 * m * 0.8706 = 1.00 g

Step 6: Solving for m: $m = \frac{{1.00}}{{0.0134 \times 0.8706}} = \frac{{1.00}}{{0.011656}} = 85.7$ g

Why other options are wrong:
- Option A: 74.6 g is incorrect. This value likely arises from an incorrect calculation of the mass fraction of Ag in Ag2S or an error in the final division.
- Option C: 107.9 g is incorrect. This value is close to the molar mass of silver and doesn't account for the percentage of argentite in the ore.
- Option D: 134.0 g is incorrect. This value might be obtained by directly dividing 1.00 g by 0.0134, neglecting the mass fraction of Ag in Ag2S.

Key Concepts:
- Stoichiometry
- Percentage composition
- Molar mass

Memory Aids:
- Remember to account for the stoichiometry of the compound when calculating mass fractions.

Quick Tips:
- Always double-check your calculations, especially when dealing with percentages and molar masses.

11 Medium

11 of 302Question permalink

Analyzing +4 | -1

In the reaction of oxalate with permanganate in acidic medium. The number of electrons involved in producing one molecule of

C{O_2}

is

View answer and explanation

Correct option: C

1

Option C (1) is correct because the oxidation of oxalate (

C_2O_4^{2-}

) to carbon dioxide (

CO_2

) involves the loss of one electron per carbon atom.

Solution approach

Correct Answer + Core Reason: 1. The oxidation of oxalate to carbon dioxide involves the loss of one electron per molecule of $CO_2$ .

Step-by-Step Solution:

Step 1: Write the half-reaction for the oxidation of oxalate to carbon dioxide.
- $C_2O_4^{2-} \to 2CO_2$

Step 2: Determine the oxidation states of carbon in oxalate and carbon dioxide.
- In $C_2O_4^{2-}$ , the oxidation state of carbon is +3.
- In $CO_2$ , the oxidation state of carbon is +4.

Step 3: Calculate the number of electrons involved in the oxidation of one oxalate ion.
- Each carbon atom changes its oxidation state from +3 to +4, which is a loss of 1 electron.
- Since there are two carbon atoms in $C_2O_4^{2-}$ , the total number of electrons lost is 2.
- $C_2O_4^{2-} \to 2CO_2 + 2e^-$

Step 4: Determine the number of electrons involved in producing one molecule of $CO_2$ .
- From the balanced half-reaction, 2 electrons are released for every 2 molecules of $CO_2$ produced.
- Therefore, 1 electron is involved in producing one molecule of $CO_2$ .

Why other options are wrong:
- Option A: 2: This is the total number of electrons released when one oxalate ion is oxidized to two carbon dioxide molecules, but the question asks for the number of electrons involved in *producing one molecule* of $CO_2$ .
- Option B: 5: This is the number of electrons involved in the reduction of permanganate ( $MnO_4^-$ ) to $Mn^{2+}$ in acidic medium, not the oxidation of oxalate.
- Option D: 10: This is incorrect and not related to the number of electrons involved in the oxidation of oxalate to carbon dioxide.

Key Concepts:
- Oxidation states
- Half-reactions
- Redox reactions

Memory Aids:
- Oxidation is Loss (of electrons), Reduction is Gain (of electrons) - OIL RIG

Quick Tips:
- Determine the oxidation states of the elements involved in the reaction.
- Balance the half-reactions to determine the number of electrons transferred.

12 Hard

12 of 302Question permalink

Understanding +4 | -1

Assertion:

\mathrm{CO}

and

\mathrm{C}_2 \mathrm{H}_2

both can be absorbed in ammoniacal

\mathrm{CuCl}

.
Reason:

\mathrm{CH}_4

is absorbed on animal charcoal.

View answer and explanation

Correct option: D

Both Assertion and Reason are correct but Reason is not correct explanation of Assertion

Option D (Both Assertion and Reason are correct but Reason is not correct explanation of Assertion) is correct because both statements are true, but unrelated.

Solution approach

Correct Answer + Core Reason: Both Assertion and Reason are correct but Reason is not correct explanation of Assertion. Both CO and C2H2 are absorbed by ammoniacal CuCl, and CH4 is absorbed by animal charcoal, but they are unrelated facts.

Step-by-Step Solution:

Step 1: Analyze the Assertion. CO and C2H2 can both form complexes with ammoniacal CuCl, leading to their absorption.

Step 2: Analyze the Reason. CH4 is a gas that can be adsorbed onto the surface of animal charcoal due to Van der Waals forces.

Step 3: Determine the relationship. The absorption of CO and C2H2 by CuCl is a chemical process, while the absorption of CH4 by animal charcoal is a physical adsorption process. They are not directly related.

Why other options are wrong:
- Option A: Assertion is correct but Reason is wrong: The Reason is also correct.
- Option B: Assertion is wrong but Reason is correct: The Assertion is also correct.
- Option C: Both Assertion and Reason are correct and Reason is correct explanation of Assertion: The Reason does not explain the Assertion.

Key Concepts:
- Absorption of gases
- Adsorption of gases
- Chemical vs. Physical processes

Memory Aids:
- Absorption involves chemical interaction; adsorption involves surface interaction.

Quick Tips:
- Distinguish between absorption and adsorption.

13 Easy

13 of 302Question permalink

Remembering +4 | -1

Molarity is expressed as:

View answer and explanation

Correct option: B

\mathrm{Mol\; litr}{\mathrm{e}^{ - 1}}

Option B is correct because molarity is defined as the number of moles of solute per liter of solution (mol/L).

Solution approach

Correct Answer + Core Reason: $\mathrm{Mol\; litr}{\mathrm{e}^{ - 1}}$ . Molarity is defined as moles of solute per liter of solution.

Step-by-Step Solution:

Step 1: Define molarity. Molarity (M) is defined as the number of moles of solute per liter of solution.

Step 2: Express molarity mathematically: Molarity = $\frac{\text{Moles of solute}}{\text{Volume of solution in liters}}$

Step 3: Identify the correct units: The units for molarity are moles per liter (mol/L) or mol L $^{-1}$ .

Why other options are wrong:
- Option A: $\mathrm{litre}\;\mathrm{mo}{\mathrm{l}^{ - 1}}$ is the inverse of molarity.
- Option C: $\mathrm{Mol}\;\mathrm{k}{\mathrm{g}^{ - 1}}$ is the unit for molality.
- Option D: $\mathrm{G}\;\mathrm{litr}{\mathrm{e}^{ - 1}}$ represents grams per liter, which is a concentration unit but not molarity.

Key Concepts:
- Molarity
- Concentration units

Memory Aids:
- Molarity = Moles / Liter

Quick Tips:
- Remember the definition of molarity and its units.

14 Hard

14 of 302Question permalink

Application +4 | -1

If the mass percentage of

\mathrm{Cu}

in an enzyme is

0.1270 \%

, then the minimum molecular mass of the enzyme will be (atomic mass of Copper

=63.54

)

View answer and explanation

Correct option: A

50,000 \mathrm{~u}

Option A (

50,000 \mathrm{~u}

) is correct because it is calculated by assuming there is one copper atom per enzyme molecule and using the mass percentage to determine the minimum molecular mass.

Solution approach

Correct Answer + Core Reason: $50,000 \mathrm{~u}$ . The minimum molecular mass is calculated assuming one copper atom per enzyme molecule.

Step-by-Step Solution:

Step 1: Define variables: Let $M$ be the minimum molecular mass of the enzyme.

Step 2: Set up the equation based on the mass percentage of copper: $\frac{{63.54}}{M} \times 100 = 0.1270$ .

Step 3: Solve for $M$ : $M = \frac{{63.54 \times 100}}{{0.1270}} = 50031.496 \approx 50,000 \mathrm{~u}$ .

Step 4: Therefore, the minimum molecular mass of the enzyme is approximately $50,000 \mathrm{~u}$ .

Why other options are wrong:
- Option B: $60,000 \mathrm{~u}$ : This is an incorrect calculation of the minimum molecular mass.
- Option C: $25,000 \mathrm{~u}$ : This is an incorrect calculation of the minimum molecular mass.
- Option D: $30,000 \mathrm{~u}$ : This is an incorrect calculation of the minimum molecular mass.

Key Concepts:
- Mass percentage
- Molecular mass
- Stoichiometry

Memory Aids:
- Mass percentage = (mass of element / mass of compound) * 100

Quick Tips:
- Assume the enzyme contains only one atom of the element to find the *minimum* molecular mass.

15 Easy

15 of 302Question permalink

Understanding +4 | -1

The law of definite proportions is not applicable to nitrogen oxide because

View answer and explanation

Correct option: C

Nitrogen equivalent weight is variable

Option C (Nitrogen equivalent weight is variable) is correct because nitrogen can exhibit different oxidation states and thus have different equivalent weights in different nitrogen oxides, violating the law of definite proportions.

Solution approach

Correct Answer + Core Reason: Nitrogen equivalent weight is variable. The law of definite proportions is violated when an element has multiple equivalent weights.

Step-by-Step Solution:

Step 1: State the Law of Definite Proportions.\nThe Law of Definite Proportions states that a given chemical compound always contains its component elements in fixed ratio (by mass) and does not depend on its source and method of preparation.

Step 2: Explain why nitrogen oxide is an exception.\nNitrogen and oxygen can combine to form various oxides such as $N_2O$ , $NO$ , $NO_2$ , $N_2O_3$ , $N_2O_5$ , etc. Because nitrogen can have different oxidation states, the ratio of nitrogen to oxygen is not fixed.

Step 3: Relate equivalent weight to the law.\nSince nitrogen can have different oxidation states, its equivalent weight varies in different oxides. This violates the law of definite proportions.

Why other options are wrong:
- Option A: Nitrogen atomic weight is constant. Atomic weight is a fundamental property of an element and does not vary.
- Option B: Nitrogen molecular weight is variable, but this is a consequence of different compounds, not a cause of the law's inapplicability.
- Option D: Oxygen atomic weight is variable is incorrect. Atomic weight is a fundamental property of an element and does not vary.

Key Concepts:
- Law of Definite Proportions
- Equivalent weight
- Oxidation states

Memory Aids:
- Remember that the Law of Definite Proportions requires fixed ratios of elements in a compound.

Quick Tips:
- Recognize that elements with variable oxidation states can lead to violations of the Law of Definite Proportions.

16 Easy

16 of 302Question permalink

Remembering +4 | -1

The least count of burette used normally in laboratory is :

View answer and explanation

Correct option: A

0.1 mL

Option A (0.1 mL) is correct because the least count of a standard laboratory burette is typically 0.1 mL.

Solution approach

Correct Answer + Core Reason: 0.1 mL. Standard laboratory burettes are graduated to 0.1 mL.

Step-by-Step Solution:

Step 1: Recall the typical markings on a burette.
- Burettes are designed for accurate dispensing of liquids.
- The graduations on a standard burette allow for readings to the nearest 0.1 mL.

Step 2: Consider the definition of least count.
- Least count is the smallest value that can be measured by an instrument.

Step 3: Conclusion: The least count of a burette used normally in the laboratory is 0.1 mL.

Why other options are wrong:
- Option B: Incorrect because 0.01 mL is too precise for a standard burette. This might be the least count of a microburette.
- Option C: Incorrect because 0.2 mL is not a standard least count for burettes.
- Option D: Incorrect because 0.02 mL is not a standard least count for burettes.

Key Concepts:
- Least count
- Volumetric analysis
- Burette

Memory Aids:
- Remember that standard burettes are graduated to 0.1 mL.

Quick Tips:
- Familiarize yourself with the common laboratory apparatus and their least counts.

17 Hard

17 of 302Question permalink

Application +4 | -1

At constant

{T}

and

{P}, 5.0 \mathrm{~L}

of

{SO}_2

are reacted with

3.0 \mathrm{~L}

of

{O}_2

according to the following equation,

2 {SO}_2(\mathrm{~g})+{O}_2(\mathrm{~g}) \rightarrow 2 {SO}_3(\mathrm{~g})

. The volume of the reaction mixture at the completion of the reaction is

View answer and explanation

Correct option: C

5.5 L

Option C (5.5 L) is correct. By identifying the limiting reactant and calculating the volume of the products and remaining reactants, we can determine the final volume of the reaction mixture.

Solution approach

Correct Answer + Core Reason: 5.5 L. The final volume is calculated by determining the limiting reactant and the volume of products formed.

Step-by-Step Solution:

Step 1: Write the balanced equation.
$2SO_2(g) + O_2(g) \rightarrow 2SO_3(g)$

Step 2: Determine the limiting reactant.\nFrom the balanced equation, 2 volumes of $SO_2$ react with 1 volume of $O_2$ .
5.0 L of $SO_2$ would require $\frac{{5.0}}{2} = 2.5 \text{{ L}}$ of $O_2$ .\nSince we have 3.0 L of $O_2$ , $SO_2$ is the limiting reactant.

Step 3: Calculate the volume of $SO_3$ produced.
2 volumes of $SO_2$ produce 2 volumes of $SO_3$ . Therefore, 5.0 L of $SO_2$ will produce 5.0 L of $SO_3$ .

Step 4: Calculate the volume of $O_2$ remaining.\nVolume of $O_2$ used = $\frac{{5.0}}{2} = 2.5 \text{{ L}}$ \nVolume of $O_2$ remaining = $3.0 - 2.5 = 0.5 \text{{ L}}$

Step 5: Calculate the total volume of the reaction mixture.\nTotal volume = Volume of $SO_3$ + Volume of $O_2$ remaining = $5.0 + 0.5 = 5.5 \text{{ L}}$

Why other options are wrong:
- Option A: Incorrect. This only considers the remaining oxygen.
- Option B: Incorrect. This is the sum of initial volumes, without considering the reaction.
- Option D: Incorrect. This is the initial volume of $SO_2$ , without considering the remaining oxygen.

Key Concepts:
- Stoichiometry
- Limiting reactant

Memory Aids:
- Limiting reactant is the reactant that is completely consumed.

Quick Tips:
- Always identify the limiting reactant first.

18 Medium

18 of 302Question permalink

Remembering +4 | -1

Molar mass is maximum for

View answer and explanation

Correct option: B

Sulphur

Option B (Sulphur) is correct because Sulphur exists as S8, which has a higher molar mass than the other options in their standard forms.

Solution approach

Correct Answer + Core Reason: Sulphur. Sulphur exists as S8, making its molar mass higher.

Step-by-Step Solution:

Step 1: Determine the molar mass of each element/molecule.

Step 2: Phosphorous usually exists as P4, Sulphur exists as S8, Copper exists as Cu (atomic), and Ozone exists as O3.

Step 3: Calculate the molar mass of each:
- P4: 4 * 31 = 124 g/mol
- S8: 8 * 32 = 256 g/mol
- Cu: 63.5 g/mol
- O3: 3 * 16 = 48 g/mol

Step 4: Compare the molar masses.

Why other options are wrong:
- Option A: Phosphorous (P4) has a molar mass of 124 g/mol, which is less than Sulphur.
- Option C: Copper (Cu) has a molar mass of 63.5 g/mol, which is less than Sulphur.
- Option D: Ozone (O3) has a molar mass of 48 g/mol, which is less than Sulphur.

Key Concepts:
- Molar mass
- Molecular formula
- Allotropy

Memory Aids:
- Remember that Sulphur exists as S8.

Quick Tips:
- Consider the molecular form of the element when calculating molar mass.

19 Easy

19 of 302Question permalink

Application +4 | -1

Which one of the followings has maximum number of atoms ?

View answer and explanation

Correct option: D

\mathrm{1}\,\,\mathrm{g}

of

\mathrm{Li}\,\left( \mathrm{s} \right)

[ Atomic mass of

Li = \mathrm{ 7}

]

Option D (

\mathrm{1}\,\mathrm{g}

of

\mathrm{Li}\,\left( \mathrm{s} \right)

) is correct because it has the highest number of moles, and therefore the largest number of atoms.

Solution approach

Correct Answer + Core Reason: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Li}\,\left( \mathrm{s} \right)$ . This contains the maximum number of atoms because it has the highest number of moles.

Step-by-Step Solution:

Step 1: Calculate the number of moles for each option using the formula: moles = mass / atomic mass.
- A: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Ag}\,\left( \mathrm{s} \right)$ : Moles = 1/108 = 0.0093 mol
- B: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Mg}\,\left( \mathrm{s} \right)$ : Moles = 1/24 = 0.0417 mol
- C: $\mathrm{1}\,\mathrm{g}$ of ${\mathrm{O}_\mathrm{2}}\,\left( \mathrm{g} \right)$ : Moles = 1/32 = 0.03125 mol. Number of atoms = 2 * 0.03125 = 0.0625 mol of atoms
- D: $\mathrm{1}\,\mathrm{g}$ of $\mathrm{Li}\,\left( \mathrm{s} \right)$ : Moles = 1/7 = 0.143 mol

Step 2: Compare the number of moles of atoms. The largest number of moles is in option D.

Step 3: Conclusion: Option D contains the maximum number of atoms.

Why other options are wrong:
- Option A: The number of moles of silver is less than that of lithium.
- Option B: The number of moles of magnesium is less than that of lithium.
- Option C: The number of moles of oxygen atoms is less than that of lithium.

Key Concepts:
- Mole concept
- Atomic mass
- Avogadro's number

Memory Aids:
- moles = mass / atomic mass

Quick Tips:
- Always convert mass to moles before comparing the number of atoms.

20 Medium

20 of 302Question permalink

Analyzing +4 | -1

A: For a given solution (density

=1 \mathrm{gm} / \mathrm{ml}

), molality is greater than molarity.

R: Molarity involves volume of solution while molality involves mass of solvent.

View answer and explanation

Correct option: A

Both A and R are correct and R is the correct explanation of A.

Option B (Both A and R are correct and R is the correct explanation of A) is incorrect. For a given solution with density = 1 g/mL, molality is less than molarity, not greater. The reason is correct, molarity involves volume of solution, while molality involves mass of solvent.

Solution approach

Correct Answer + Core Reason: Both A and R are correct and R is the correct explanation of A. Molality is usually greater than molarity for dilute solutions with density close to 1 g/mL because the mass of solvent is less than the volume of solution.

Step-by-Step Solution:

Step 1: Define Molarity and Molality.\nMolarity (M) = moles of solute / volume of solution (in liters)\nMolality (m) = moles of solute / mass of solvent (in kg)

Step 2: Analyze Assertion (A): For a given solution (density = 1 gm/ml), molality is greater than molarity.\nIf the density of the solution is 1 g/mL, then 1 liter of solution weighs 1000 g. However, the solution consists of both solute and solvent. Therefore, the mass of the solvent will be less than 1000 g (1 kg). Since molality uses the mass of the solvent in the denominator, and molarity uses the volume of the solution, molality will be greater than molarity when the density is 1 g/mL.

Step 3: Analyze Reason (R): Molarity involves volume of solution while molality involves mass of solvent.\nThis statement is correct. Molarity is defined as moles of solute per liter of solution, while molality is defined as moles of solute per kilogram of solvent.

Step 4: Determine if the reason is the correct explanation for the assertion.\nThe reason correctly explains why the assertion is true. Because molality uses the mass of the solvent and molarity uses the volume of the solution, and the mass of the solvent is less than the volume of the solution when density is 1 g/mL, molality is greater than molarity.

Why other options are wrong:
- Option B (Both A and R are correct, but R is not the correct explanation of A): The reason is the correct explanation.
- Option C (A is correct but R is incorrect): Both A and R are correct.
- Option D (Both the A and R are incorrect): Both A and R are correct.

Key Concepts:
- Molarity
- Molality
- Density

Memory Aids:
- Molarity = moles/Liter of solution
- Molality = moles/kg of solvent

Quick Tips:
- Remember the definitions of molarity and molality and how they relate to the volume of solution and mass of solvent.

21 Medium

21 of 302Question permalink

Application +4 | -1

There are two isotopes of an element with atomic massz. Heavier one has atomic mass

z + 2

and lighter one has

z -1

, the abundance of lighter one is

View answer and explanation

Correct option: A

66.6\%

Option A (

66.6\%

) is correct because it is calculated using the weighted average formula for atomic mass, solving for the abundance of the lighter isotope.

Solution approach

Correct Answer + Core Reason: $66.6\%$ . The abundance is calculated using the weighted average formula for atomic mass.

Step-by-Step Solution:

Step 1: Define variables: Let $x$ be the abundance of the lighter isotope ( $z-1$ ) and $(1-x)$ be the abundance of the heavier isotope ( $z+2$ ).

Step 2: Write the equation for the average atomic mass: $z = x(z-1) + (1-x)(z+2)$ .

Step 3: Expand the equation: $z = xz - x + z + 2 - xz - 2x$ .

Step 4: Simplify the equation: $z = z + 2 - 3x$ .

Step 5: Solve for $x$ : $0 = 2 - 3x \Rightarrow 3x = 2 \Rightarrow x = \frac{{2}}{{3}}$ .

Step 6: Convert $x$ to percentage: $x = \frac{{2}}{{3}} \times 100\% = 66.6\%$ .

Step 7: Therefore, the abundance of the lighter isotope is $66.6\%$ .

Why other options are wrong:
- Option B: $69.7\%$ : This is an incorrect calculation of the abundance.
- Option C: $6.67\%$ : This is an incorrect calculation of the abundance and likely a misunderstanding of the problem.
- Option D: $33.3\%$ : This is the abundance of the heavier isotope, not the lighter one.

Key Concepts:
- Isotopes
- Average atomic mass
- Weighted average

Memory Aids:
- Average atomic mass = (abundance of isotope 1 * mass of isotope 1) + (abundance of isotope 2 * mass of isotope 2) + ...

Quick Tips:
- Remember that the sum of the abundances of all isotopes must equal 1 or 100%.

22 Easy

22 of 302Question permalink

Application +4 | -1

The normality of one molar sodium carbonate solution is:

View answer and explanation

Correct option: A

2

Option A (2) is correct because the normality of sodium carbonate is twice its molarity due to its n-factor being 2.

Solution approach

Correct Answer + Core Reason: 2. The normality of sodium carbonate is twice its molarity because it can react with two moles of $H^+$ ions.

Step-by-Step Solution:

Step 1: Write the formula for sodium carbonate.\nThe formula for sodium carbonate is $Na_2CO_3$ .

Step 2: Determine the n-factor for sodium carbonate.\nSodium carbonate can react with two moles of $H^+$ ions: $Na_2CO_3 + 2HCl \rightarrow 2NaCl + H_2O + CO_2$ . Therefore, the n-factor is 2.

Step 3: Calculate the normality.\nNormality (N) = Molarity (M) x n-factor = 1 M x 2 = 2 N

Why other options are wrong:
- Option B: 1: This is incorrect because it assumes the normality is equal to the molarity, which is only true for substances with an n-factor of 1.
- Option C: $0.5$ : This is incorrect because it divides the molarity by 2, which is the opposite of what should be done to find the normality.
- Option D: $1.5$ : This is incorrect because it uses an incorrect n-factor or performs an incorrect calculation.

Key Concepts:
- Normality
- Molarity
- n-factor (basicity/acidity)

Memory Aids:
- Normality = Molarity x n-factor

Quick Tips:
- Always determine the n-factor based on the number of replaceable $H^+$ or $OH^-$ ions or the number of electrons transferred in a reaction.

23 Easy

23 of 302Question permalink

Understanding +4 | -1

Given P = 0.0030m, Q = 2.40m, R = 3000m, Significant figures in P, Q and R are respectively

View answer and explanation

Correct option: B

2, 3, 4

Option B is correct because significant figures are counted from the first non-zero digit, and trailing zeros without a decimal point are ambiguous.

Solution approach

Correct Answer + Core Reason: 2, 3, 4. The number of significant figures is determined by the rules for counting them.

Step-by-Step Solution:

Step 1: Recall the rules for significant figures.

Step 2: For P = 0.0030m, the leading zeros are not significant, so there are 2 significant figures (3 and 0).

Step 3: For Q = 2.40m, all digits are significant, so there are 3 significant figures.

Step 4: For R = 3000m, trailing zeros without a decimal point are ambiguous, but we assume they are significant because the number is written as 3000m, implying measurement to the nearest meter. So, there are 4 significant figures.

Step 5: Final Answer: 2, 3, 4.

Why other options are wrong:
- Option A: 2, 2, 1 is incorrect.
- Option C: 4, 2, 1 is incorrect.
- Option D: 4, 2, 3 is incorrect.

Key Concepts:
- Significant figures
- Rules for significant figures

Memory Aids:
- Remember the rules for counting significant figures.

Quick Tips:
- Pay attention to leading and trailing zeros and the presence of a decimal point.

24 Hard

24 of 302Question permalink

Analyzing +4 | -1

Choose the corrcct statements.

(a) Double decomposition method is based on the law of equivalent.

(b) For a reaction,

{P}_{m} {Q}_{{n}}+{R}_o {S}_{{p}} \longrightarrow \text{products}

If amount of

P_m Q_n

reactcd

=w_1

gm

and amount of

R_o S_p

reacted

=w_2

gm, then

\frac{w_1}{w_2}=\frac{\text {Equivalent wt. of } R_o S_p}{\text {Equivalent wt. of } P_{m} Q_{n}}

(c) For a rcaction

P_{m} Q_n+R_o S_p \longrightarrow \text{products}

If amount of

P_m Q_n

reacted

=w_1

gm

and amount of

R_o S_p

reacted

=w_2

gm, then

\frac{w_1}{w_2}=\frac{\text {Equivalent wt. of } P_m Q_n}{\text {Equivalent wt. of } R_o S_p}

(d) 1 equivalent of oxygen

=16 \mathrm{~gm}

View answer and explanation

Correct option: D

a and c are correct

Option D (a and c are correct) is correct because double decomposition reactions are based on the law of equivalents, and the ratio of reacted masses is equal to the ratio of their equivalent weights.

Solution approach

Correct Answer + Core Reason: a and c are correct. Double decomposition reactions are based on the law of equivalents, and the mass ratio equals the equivalent weight ratio.

Step-by-Step Solution:

Step 1: Analyze statement (a): Double decomposition method is based on the law of equivalent.
- This statement is correct. Double decomposition reactions involve the exchange of ions, and the law of equivalents states that substances react in the ratio of their equivalent weights.

Step 2: Analyze statement (b): For a reaction, ${P}_{m} {Q}_{{n}}+{R}_o {S}_{{p}} \longrightarrow \text{products}$ If amount of $P_m Q_n$ reacted $=w_1$ gm and amount of $R_o S_p$ reacted $=w_2$ gm, then $\frac{w_1}{w_2}=\frac{\text {Equivalent wt. of } R_o S_p}{\text {Equivalent wt. of } P_{m} Q_{n}}$
- This statement is incorrect. The ratio should be inverse.

Step 3: Analyze statement (c): For a reaction $P_{m} Q_n+R_o S_p \longrightarrow \text{products}$ If amount of $P_m Q_n$ reacted $=w_1$ gm and amount of $R_o S_p$ reacted $=w_2$ gm, then $\frac{w_1}{w_2}=\frac{\text {Equivalent wt. of } P_m Q_n}{\text {Equivalent wt. of } R_o S_p}$
- This statement is correct. The ratio of the masses reacted is equal to the ratio of their equivalent weights.

Step 4: Analyze statement (d): 1 equivalent of oxygen $=16 \mathrm{~gm}$
- This statement is incorrect. The equivalent weight of oxygen is 8 g (16 g / valency of 2).

Step 5: Conclusion: Statements (a) and (c) are correct.

Why other options are wrong:
- Option A: Incorrect because statement (b) is incorrect and statement (d) is incorrect.
- Option B: Incorrect because statement (b) is incorrect and statement (d) is incorrect.
- Option C: Incorrect because statement (b) is incorrect and statement (d) is incorrect.

Key Concepts:
- Law of equivalents
- Double decomposition reactions
- Equivalent weight

Memory Aids:
- Remember that substances react in the ratio of their equivalent weights.

Quick Tips:
- Understand the law of equivalents and its application in chemical reactions.

25 Medium

25 of 302Question permalink

Application +4 | -1

0.2

g of a sample of

{\mathrm{H}_2}{\mathrm{O}_2}

required

10

mL of

N\mathrm{KMn}{\mathrm{O}_4}

in a titration in the presence of

{\mathrm{H}_2}\mathrm{S}{\mathrm{O}_4}\mathrm{.}

. Purity of

{\mathrm{H}_2}{\mathrm{O}_2}

is :

View answer and explanation

Correct option: B

85\%

Option B (

85\%

) is correct because it is the correct purity of H2O2 calculated using the titration data and stoichiometry.

Solution approach

Correct Answer + Core Reason: $85\%$ . The purity of ${\mathrm{H}_2}{\mathrm{O}_2}$ is calculated using the titration data and stoichiometry.

Step-by-Step Solution:

Step 1: Write the balanced redox reaction.
$2KMnO_4 + 5H_2O_2 + 3H_2SO_4 \rightarrow K_2SO_4 + 2MnSO_4 + 8H_2O + 5O_2$

Step 2: Calculate the milliequivalents of $KMnO_4$ .\nMilliequivalents of $KMnO_4 = Normality \times Volume (in mL) = 1 N \times 10 mL = 10$ meq

Step 3: Calculate the milliequivalents of $H_2O_2$ .\nMilliequivalents of $H_2O_2$ = Milliequivalents of $KMnO_4 = 10$ meq

Step 4: Calculate the mass of $H_2O_2$ .\nEquivalent weight of $H_2O_2 = \frac{{Molar mass}}{{n - factor}} = \frac{{34}}{2} = 17$ g/eq\nMilliequivalent weight of $H_2O_2 = 17$ mg/meq\nMass of $H_2O_2 = Milliequivalents \times Milliequivalent weight =$ 10 meq × 17 mg/meq = 170 mg = 0.17 g $\n\n**Step 5:** Calculate the purity of$ H_2O_2 $.\nPurity =$ $\frac{{Mass of H_2O_2}}{{Mass of sample}}$ × 100 = $\frac{{0.17 g}}{{0.2 g}}$ × 100 = 85\% $\n\n**Why other options are wrong:**\n- **Option A:**$ 25\% $: This is incorrect because it uses an incorrect calculation based on the titration data or stoichiometry.\n- **Option C:**$ 65\% $: This is incorrect because it uses an incorrect calculation based on the titration data or stoichiometry.\n- **Option D:**$ 95\% $: This is incorrect because it uses an incorrect calculation based on the titration data or stoichiometry.\n\n**Key Concepts:**\n- Redox titrations\n- Normality\n- Equivalent weight\n- Stoichiometry\n\n**Memory Aids:**\n- Milliequivalents = Normality x Volume (in mL)\n\n**Quick Tips:**\n- Always balance the redox reaction before performing stoichiometric calculations.\n- Ensure correct units are used in calculations.$

26 Easy

26 of 302Question permalink

Understanding +4 | -1

Both natural and synthetic sample of cupric carbonate contains same percentage of copper and carbon by mass. This fact is based on

View answer and explanation

Correct option: B

Law of definite proportion

The correct answer is B (Law of definite proportion) because a given compound always contains exactly the same proportion of elements by mass, regardless of its source.

Solution approach

Correct Answer + Core Reason: Law of definite proportion. A given compound always contains exactly the same proportion of elements by mass.

Step-by-Step Solution:

Step 1: Define the Law of Definite Proportions: A chemical compound always contains its constituent elements in a fixed ratio (by mass) and does not depend on its source or method of preparation.

Step 2: The problem states that both natural and synthetic cupric carbonate contain the same percentage of copper and carbon by mass.

Step 3: This directly illustrates the Law of Definite Proportions.

Why other options are wrong:
- Option A: Law of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. This is not directly illustrated by the given information.
- Option C: Law of multiple proportions deals with different compounds formed by the same elements. This is not relevant here.
- Option D: Dalton’s atomic theory provides the basis for understanding chemical combinations but is not the most direct explanation for the observation.

Key Concepts:
- Law of definite proportion

Memory Aids:
- Definite proportion: fixed ratio in a compound.

Quick Tips:
- Focus on the fixed ratio of elements in a given compound.

27 Easy

27 of 302Question permalink

Application +4 | -1

Maximum number of atoms are present in

View answer and explanation

Correct option: A

8g\,C{H_4}

Option A (

8g\,C{H_4}

) is correct because it contains the highest number of moles of molecules, and each molecule has a significant number of atoms.

Solution approach

Correct Answer + Core Reason: $8g\,C{H_4}$ . It contains the maximum number of atoms due to the highest number of moles and atoms per molecule.

Step-by-Step Solution:

Step 1: Calculate the number of moles for each option.

Step 2: Option A: $C{H_4}$ (Molar mass = 12 + 4 = 16 g/mol). Moles = $\frac{{8}}{{16}} = 0.5$ mol. Number of atoms per molecule = 1 (C) + 4 (H) = 5. Total atoms = 0.5 mol * 5 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $1.5055 \times 10^{24}$ atoms.

Step 3: Option B: ${C_6}{H_{12}}{O_6}$ (Molar mass = 6(12) + 12(1) + 6(16) = 72 + 12 + 96 = 180 g/mol). Moles = $\frac{{18}}{{180}} = 0.1$ mol. Number of atoms per molecule = 6 (C) + 12 (H) + 6 (O) = 24. Total atoms = 0.1 mol * 24 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $1.44528 \times 10^{23}$ atoms.

Step 4: Option C: $CaC{O_3}$ (Molar mass = 40 + 12 + 3(16) = 40 + 12 + 48 = 100 g/mol). Moles = $\frac{{25}}{{100}} = 0.25$ mol. Number of atoms per molecule = 1 (Ca) + 1 (C) + 3 (O) = 5. Total atoms = 0.25 mol * 5 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $7.5275 \times 10^{23}$ atoms.

Step 5: Option D: $CO$ (Molar mass = 12 + 16 = 28 g/mol). Moles = $\frac{{28}}{{28}} = 1$ mol. Number of atoms per molecule = 1 (C) + 1 (O) = 2. Total atoms = 1 mol * 2 atoms/molecule * $6.022 \times 10^{23}$ atoms/mol = $1.2044 \times 10^{24}$ atoms.

Step 6: Compare the total number of atoms for each option. Option A has the highest number of atoms.

Why other options are wrong:
- Option B: Although ${C_6}{H_{12}}{O_6}$ has a large number of atoms per molecule, the number of moles is small, resulting in fewer total atoms than $C{H_4}$ .
- Option C: $CaC{O_3}$ has a relatively small number of moles and atoms per molecule, leading to fewer total atoms than $C{H_4}$ .
- Option D: $CO$ has a large number of moles, but only two atoms per molecule, resulting in fewer total atoms than $C{H_4}$ .

Key Concepts:
- Mole concept
- Avogadro's number
- Molar mass

Memory Aids:
- Remember that the number of atoms is proportional to the number of moles and the number of atoms per molecule.

Quick Tips:
- Calculate the number of moles for each compound.
- Multiply the number of moles by the number of atoms in each molecule and Avogadro's number to find the total number of atoms.

28 Medium

28 of 302Question permalink

Remembering +4 | -1

Number of significant figures in 3.06 is

View answer and explanation

Correct option: D

3

Option D (3) is correct because in 3.06, all digits are significant, including the zero between the 3 and the 6.

Solution approach

Correct Answer + Core Reason: 3. All digits in 3.06 are significant.

Step-by-Step Solution:

Step 1: Recall the rules for significant figures.

Step 2: Non-zero digits are always significant.

Step 3: Zeros between non-zero digits are significant.

Step 4: Leading zeros are not significant.

Step 5: Trailing zeros are significant only if the number contains a decimal point.

Step 6: In 3.06, 3 and 6 are non-zero and significant. The 0 is between two non-zero digits and is therefore significant.

Step 7: Therefore, 3.06 has 3 significant figures.

Why other options are wrong:
- Option A: 6 is incorrect. It seems to consider all the digits as significant without considering the rules.
- Option B: 8 is incorrect. There are only three digits in the number.
- Option C: 4 is incorrect. There are only three digits in the number, and all are significant.

Key Concepts:
- Significant figures
- Rules for significant figures

Memory Aids:
- Atlantic-Pacific rule for significant figures (if the decimal is Absent, start counting from the Atlantic (right) side at the first non-zero digit; if the decimal is Present, start counting from the Pacific (left) side at the first non-zero digit). In this case, decimal is present, so start from left.

Quick Tips:
- Always remember the rules for determining significant figures.

29 Medium

29 of 302Question permalink

Understanding +4 | -1

The equivalent weight of an acid is obtained by dividing its mol. wt. by its:

View answer and explanation

Correct option: B

Basicity

The correct answer is B (Basicity) because the equivalent weight of an acid is calculated by dividing its molecular weight by its basicity.

Solution approach

Correct Answer + Core Reason: Basicity. Equivalent weight of an acid is its molecular weight divided by its basicity.

Step-by-Step Solution:

Step 1: Define equivalent weight of an acid: Equivalent weight = $\frac{{\text{{Molecular weight}}}}{{\text{{Basicity}}}}$

Step 2: The question asks what we divide the molecular weight by to get the equivalent weight.

Step 3: From the definition, it's the basicity.

Step 4: Final Answer: Basicity

Why other options are wrong:
- Option A: Acidity is a property of acids, but it's not directly used in the calculation of equivalent weight.
- Option C: pH is a measure of the acidity or alkalinity of a solution and is not directly related to the equivalent weight of an acid.
- Option D: The correct answer is one of the options.

Key Concepts:
- Equivalent weight of an acid
- Basicity of an acid

Memory Aids:
- Equivalent weight = (Molecular weight) / (Basicity)

Quick Tips:
- Remember the definition of equivalent weight.

30 Easy

30 of 302Question permalink

Analyzing +4 | -1

An amount of 5 moles of

\text{A,}

6 moles of

\text{B}

and excess amount of

\mathrm{C}

are mixed to produce a final product

\mathrm{D}

, according to the following reactions.

\begin{aligned} & \mathrm{A}+2 \mathrm{B} \rightarrow \mathrm{I} \\ & \mathrm{I}+\mathrm{C} \rightarrow \mathrm{B}+\mathrm{D} \end{aligned}

What is the maximum moles of

\mathrm{D},

which can be produced assuming that the products formed can also be reused in the reactions?

View answer and explanation

Correct option: C

5 moles

Option C (5 moles) is correct. Since B is regenerated in the second reaction, A is the limiting reactant, and the maximum moles of D produced will be equal to the initial moles of A.

Solution approach

Correct Answer + Core Reason: 5 moles. Since B is regenerated, A is the limiting reactant, and moles of D produced equals moles of A.

Step-by-Step Solution:

Step 1: Analyze the reactions.
$A + 2B \rightarrow I$
$I + C \rightarrow B + D$

Step 2: Determine the limiting reactant.\nInitially, we have 5 moles of A and 6 moles of B. According to the first reaction, 1 mole of A reacts with 2 moles of B. So, 5 moles of A would require 10 moles of B. Since we only have 6 moles of B, B is the limiting reactant for the first reaction. However, B is regenerated in the second reaction, so we need to consider the overall reaction.

Step 3: Combine the reactions to find the overall reaction.\nMultiply the second reaction by 2: $2I + 2C \rightarrow 2B + 2D$ \nNow, multiply the first reaction by 2: $2A + 4B \rightarrow 2I$ \nSubstitute 2I from the second equation into the first: $2A + 4B + 2C \rightarrow 2B + 2D$ \nSimplify: $2A + 2B + 2C \rightarrow 2D$ \nDivide by 2: $A + B + C \rightarrow D$

Step 4: Determine the limiting reactant for the overall reaction.\nSince C is in excess, we only need to consider A and B. We have 5 moles of A and 6 moles of B. According to the overall reaction, 1 mole of A reacts with 1 mole of B. Therefore, A is the limiting reactant.

Step 5: Calculate the maximum moles of D produced.\nSince A is the limiting reactant, the maximum moles of D produced will be equal to the initial moles of A, which is 5 moles.

Why other options are wrong:
- Option A: Incorrect because it assumes B is the limiting reactant without considering it is regenerated.
- Option B: Incorrect because it is not based on the stoichiometry of the reaction and the limiting reactant.
- Option D: Incorrect because it assumes B is the limiting reactant without considering it is regenerated.

Key Concepts:
- Stoichiometry
- Limiting reactant

Memory Aids:
- The limiting reactant is the reactant that is completely consumed in a reaction.

Quick Tips:
- When a reactant is regenerated in a subsequent reaction, consider the overall reaction to determine the limiting reactant.

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