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NEET • CHEMISTRY • REDOX REACTIONS

Redox reactions practice · Easy

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61 Easy

61 of 65Question permalink

Analyzing +4 | -1

In which reaction change in oxidation number of underlined atom is maximum when all of them react with

C{l_2}

water:-

View answer and explanation

Correct option: D

\underline {{I_2}}

Option D (I2) is correct because iodine can be oxidized from 0 to +7, resulting in a maximum change of +7 in oxidation number.

Solution approach

Correct Answer + Core Reason: I2. The change in oxidation number is maximum for I2 when it reacts with Cl2 water.

Step-by-Step Solution:

Step 1: Determine the oxidation number of the underlined atom in each species:
- FeSO4: Fe = +2
- Na2SO3: S = +4
- SO2: S = +4
- I2: I = 0

Step 2: Determine the maximum oxidation number that each atom can achieve:
- Fe: +3
- S: +6
- I: +7

Step 3: Calculate the maximum change in oxidation number for each atom:
- Fe: +3 - (+2) = 1
- S in Na2SO3: +6 - (+4) = 2
- S in SO2: +6 - (+4) = 2
- I: +7 - 0 = 7

Step 4: Compare the changes in oxidation number. The maximum change is 7 for iodine.

Why other options are wrong:
- Option A (FeSO4(Aq)): The change in oxidation number of Fe is only 1.
- Option B (Na2SO3(Aq)): The change in oxidation number of S is 2.
- Option C (SO2): The change in oxidation number of S is 2.

Key Concepts:
- Oxidation number rules
- Oxidation and reduction

Memory Aids:
- Oxidation is loss of electrons, reduction is gain of electrons (OIL RIG).

Quick Tips:
- Determine the initial and maximum possible oxidation numbers to find the maximum change.

62 Easy

62 of 65Question permalink

Remembering +4 | -1

A group of methods of quantitative chemical analysis involving the measurement of volume of reacting substance is known as :

View answer and explanation

Correct option: B

Volumetric analysis

Option B (Volumetric analysis) is correct because volumetric analysis involves measuring the volume of reacting substances to determine the quantity of an analyte.

Solution approach

Correct Answer + Core Reason: Volumetric analysis. This method uses volume measurements of reacting substances for quantitative analysis.

Step-by-Step Solution:

Step 1: Define quantitative chemical analysis: Determining the amount or concentration of a substance.

Step 2: Define volumetric analysis: A quantitative analysis method based on measuring the volume of a solution of known concentration that is required to react completely with the analyte.

Step 3: Define gravimetric analysis: A quantitative analysis method based on determining the mass of a substance.

Step 4: Relate the definition to the question. The question specifically asks about methods involving volume measurement.

Why other options are wrong:
- Option A: Gravimetric analysis: This involves measuring mass, not volume.
- Option C: Both (a) and (b): This is incorrect because the question specifically asks about volume measurement, which is only volumetric analysis.
- Option D: None of the above: This is incorrect because volumetric analysis is a valid method.

Key Concepts:
- Quantitative Chemical Analysis
- Volumetric Analysis
- Gravimetric Analysis

Memory Aids:
- Volume = Volumetric
- Grams = Gravimetric

Quick Tips:
- Understand the fundamental differences between volumetric and gravimetric analysis.

63 Easy

63 of 65Question permalink

Understanding +4 | -1

Which does not form two or more chlorides?

View answer and explanation

Correct option: A

Option A (NA) is correct because sodium only exhibits a +1 oxidation state and therefore can only form one chloride, NaCl.

Solution approach

Correct Answer + Core Reason: NA. Sodium only exhibits a +1 oxidation state.

Step-by-Step Solution:

Step 1: Recall the common oxidation states of the given elements.

Step 2: Sodium (Na) is an alkali metal and typically exhibits only a +1 oxidation state.

Step 3: Mercury (Hg), Copper (Cu) and Iron (Fe) can exhibit multiple oxidation states and form more than one chloride (e.g., HgCl₂, Hg₂Cl₂, CuCl, CuCl₂, FeCl₂, FeCl₃).

Step 4: Therefore, Na does not form two or more chlorides.

Why other options are wrong:
- Option B: Mercury can form HgCl₂ and Hg₂Cl₂.
- Option C: Copper can form CuCl and CuCl₂.
- Option D: Iron can form FeCl₂ and FeCl₃.

Key Concepts:
- Oxidation states
- Alkali metals
- Transition metals

Memory Aids:
- Remember that alkali metals typically have only one oxidation state (+1).

Quick Tips:
- Know the common oxidation states of common elements.

64 Easy

64 of 65Question permalink

Analyzing +4 | -1

Which is not a redox reaction?

View answer and explanation

Correct option: B

\mathrm{N}{\mathrm{H}_4}\mathrm{Cl} \to \mathrm{N}{\mathrm{H}_3} + \mathrm{HCl}

Option B (

\mathrm{N}{\mathrm{H}_4}\mathrm{Cl} \to \mathrm{N}{\mathrm{H}_3} + \mathrm{HCl}

) is correct because there is no change in the oxidation state of any element in this reaction.

Solution approach

Correct Answer + Core Reason: $\mathrm{N}{\mathrm{H}_4}\mathrm{Cl} \to \mathrm{N}{\mathrm{H}_3} + \mathrm{HCl}$ . This is a decomposition reaction where no oxidation state changes occur.

Step-by-Step Solution:

Step 1: Determine the oxidation states of each element in the reactants and products.

Step 2: In $\mathrm{N}{\mathrm{H}_4}\mathrm{Cl}$ , N is -3, H is +1, and Cl is -1.

Step 3: In $\mathrm{N}{\mathrm{H}_3}$ , N is -3 and H is +1. In $\mathrm{HCl}$ , H is +1 and Cl is -1.

Step 4: Compare the oxidation states of each element on both sides of the equation. No element has changed its oxidation state.

Step 5: Since there is no change in oxidation state, this is not a redox reaction.

Why other options are wrong:
- Option A: ${\mathrm{H}_2} + \mathrm{B}{\mathrm{r}_2} \to 2\mathrm{HBr}$ : H goes from 0 to +1 (oxidation) and Br goes from 0 to -1 (reduction).
- Option C: $\mathrm{N}{\mathrm{H}_4}\mathrm{N}{\mathrm{O}_3} \to {\mathrm{N}_2}\mathrm{O} + 2{\mathrm{H}_2}\mathrm{O}$ : N in $\mathrm{N}{\mathrm{H}_4}^+$ goes from -3 to +1 (oxidation) and N in $\mathrm{N}{\mathrm{O}_3}^-$ goes from +5 to +1 (reduction).
- Option D: $\mathrm{Fe} + \mathrm{S} \to \mathrm{FeS}$ : Fe goes from 0 to +2 (oxidation) and S goes from 0 to -2 (reduction).

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

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

Quick Tips:
- Look for changes in oxidation states to identify redox reactions. If no oxidation state changes, it is not a redox reaction.

65 Easy

65 of 65Question permalink

Remembering +4 | -1

Oxidation number of Sulphur in

{S_8}

View answer and explanation

Correct option: A

zero

Option A (zero) is correct because in elemental form, the oxidation number of any element is zero.

Solution approach

Correct Answer + Core Reason: zero. The oxidation number of an element in its elemental form is always zero.

Step-by-Step Solution:

Step 1: Identify the element: Sulphur (S) in the form S8.

Step 2: Recall the rule: The oxidation number of an element in its elemental form is zero.

Step 3: Apply the rule: Since S8 is the elemental form of sulphur, its oxidation number is zero.

Step 4: Final Answer: 0

Why other options are wrong:
- Option B (-2): This is the common oxidation state of sulphur in some compounds, but not in its elemental form.
- Option C (+8): This is incorrect as sulphur cannot have +8 oxidation state in S8.
- Option D (+2): This is incorrect as sulphur cannot have +2 oxidation state in S8.

Key Concepts:
- Oxidation number rules
- Oxidation state of elements in elemental form

Memory Aids:
- Elements in their standard state have an oxidation number of zero.

Quick Tips:
- Always remember the oxidation number rules when assigning oxidation states.

Revision notes and key takeaways

Review REDOX REACTIONS in your textbook or class notes, then use this set to check your understanding.

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