STRUCTURE OF ATOM MCQs for NEET UG CHEMISTRY — Easy, Page 6

151 Easy

Remembering +4 | -1

Mass of an electron is :

View answer and explanation

Correct option: A

9.1 \times {10^{ - 28}}\mathrm{g}

Option A is correct because the mass of an electron is approximately

9.1 \times {10^{ - 28}}\mathrm{g}

.

Solution approach

Correct Answer + Core Reason: $9.1 \times {10^{ - 28}}\mathrm{g}$ . The mass of an electron is approximately $9.1 \times {10^{ - 28}}\mathrm{g}$ .

Step-by-Step Solution:

Step 1: Recall the mass of an electron.

Step 2: Identify the correct value from the given options.

Step 3: The mass of an electron is $9.1 \times {10^{ - 28}}\mathrm{g}$ .

Why other options are wrong:
- Option B: $9.1 \times {10^{ - 25}}\mathrm{g}$ is incorrect.
- Option C: $9.1 \times {10^{ - 10}}\mathrm{g}$ is incorrect.
- Option D: $9.1 \times {10^{ - 18}}\mathrm{g}$ is incorrect.

Key Concepts:
- Mass of an electron

Memory Aids:
- Remember the mass of an electron.

Quick Tips:
- Know the mass of an electron.

152 Easy

152 of 176Question permalink

Application +4 | -1

The total number of fundamental particles in one atom of

\;_6^{14}\mathrm{C}

is:

View answer and explanation

Correct option: D

20

Option D (20) is correct because it represents the total number of protons, neutrons, and electrons in the carbon atom.

Solution approach

Correct Answer + Core Reason: 20. The total number of fundamental particles is the sum of protons, neutrons, and electrons.

Step-by-Step Solution:

Step 1: The notation $\;_6^{14}\mathrm{C}$ indicates that the atom has an atomic number of 6 and a mass number of 14.

Step 2: The atomic number (6) represents the number of protons in the nucleus. In a neutral atom, the number of electrons is equal to the number of protons, so there are 6 electrons.

Step 3: The mass number (14) represents the total number of protons and neutrons in the nucleus. Therefore, the number of neutrons is 14 - 6 = 8.

Step 4: The total number of fundamental particles (protons, neutrons, and electrons) is 6 (protons) + 8 (neutrons) + 6 (electrons) = 20.

Why other options are wrong:
- Option A: Only counts protons.
- Option B: Only counts neutrons.
- Option C: Only counts protons and neutrons (mass number).

Key Concepts:
- Atomic number
- Mass number
- Protons, neutrons, and electrons

Memory Aids:
- Atomic number = number of protons
- Mass number = number of protons + number of neutrons

Quick Tips:
- Remember that in a neutral atom, the number of protons equals the number of electrons.

153 Easy

153 of 176Question permalink

Application +4 | -1

An atom emits energy equal to

4 \times {10^{ - 12}}\mathrm{erg}.

. To which part of electromagnetic spectrum it belongs?

View answer and explanation

Correct option: B

Visible region

Option B is correct. An energy of 4 × 10^-12 erg corresponds to wavelengths in the visible region of the electromagnetic spectrum.

Solution approach

Correct Answer + Core Reason: Visible region. The calculated wavelength falls within the visible region of the electromagnetic spectrum.

Step-by-Step Solution:

Step 1: Convert energy to Joules: $4 \times 10^{-12} \text{ erg} = 4 \times 10^{-19} \text{ J}$ (since 1 erg = $10^{-7}$ J).

Step 2: Calculate the wavelength using $E = \frac{hc}{\lambda}$ : $\lambda = \frac{hc}{E}$ , where $h = 6.626 \times 10^{-34} \text{ Js}$ and $c = 3 \times 10^8 \text{ m/s}$ .

Step 3: Substitute the values: $\lambda = \frac{(6.626 \times 10^{-34} \text{ Js})(3 \times 10^8 \text{ m/s})}{4 \times 10^{-19} \text{ J}} = \frac{19.878 \times 10^{-26}}{4 \times 10^{-19}} \text{ m} = 4.97 \times 10^{-7} \text{ m} = 497 \text{ nm}$ .

Step 4: Determine the region: A wavelength of 497 nm falls within the visible region (approximately 400-700 nm).

Why other options are wrong:
- Option A: UV region: Incorrect because UV region has shorter wavelengths than 497 nm.
- Option C: IR region: Incorrect because IR region has longer wavelengths than 497 nm.
- Option D: Microwave region: Incorrect because microwave region has much longer wavelengths than 497 nm.

Key Concepts:
- Electromagnetic spectrum
- Energy of a photon
- Wavelength

Memory Aids:
- Remember the order of the electromagnetic spectrum (Radio, Microwave, IR, Visible, UV, X-ray, Gamma).

Quick Tips:
- Convert energy to Joules and wavelength to meters before using the formula. Know the approximate wavelength ranges for different regions of the electromagnetic spectrum.

154 Easy

154 of 176Question permalink

Analyzing +4 | -1

Statement I : Chemical properties of atoms are controlled by the number of protons, which are determined by the number of electrons in the valence shell.
Statement II : The number of proton is equal to the number of electron in an electrically neutral atom

View answer and explanation

Correct option: D

Statement II is correct but Statement I is incorrect

Statement II is correct because in an electrically neutral atom, the number of protons equals the number of electrons. Statement I is incorrect because chemical properties are primarily determined by the number of electrons in the valence shell, not the number of protons directly.

Solution approach

Correct Answer + Core Reason: Statement II is correct but Statement I is incorrect. Chemical properties are determined by valence electrons, and neutral atoms have equal protons and electrons.

Step-by-Step Solution:

Step 1: Analyze Statement I: Chemical properties are determined by the electron configuration, specifically the valence electrons, which dictate how an atom interacts with other atoms. While the number of protons defines the element, it's the electrons that govern the chemical behavior.

Step 2: Analyze Statement II: In a neutral atom, the positive charge of the protons in the nucleus is balanced by the negative charge of the electrons orbiting the nucleus. Therefore, the number of protons must equal the number of electrons for the atom to be electrically neutral.

Step 3: Conclusion: Statement I is incorrect because it emphasizes protons over valence electrons in determining chemical properties. Statement II is correct because it accurately describes the charge balance in a neutral atom.

Why other options are wrong:
- Option A: Both statements are not correct. Statement I is incorrect.
- Option B: Both statements are not incorrect. Statement II is correct.
- Option C: Statement I is not correct, and Statement II is correct, so this option is incorrect.

Key Concepts:
- Atomic Structure
- Chemical Properties
- Valence Electrons
- Neutral Atoms

Memory Aids:
- "Electrons are everything in chemical reactions!"
- "Neutral = Protons = Electrons"

Quick Tips:
- Remember that valence electrons are the key to chemical behavior.
- Always consider charge balance when dealing with atoms and ions.

155 Easy

155 of 176Question permalink

Application +4 | -1

The total number of electrons present in all the ‘s’ orbitals, all the ‘p’ orbitals and all the ‘d’ orbitals of cesium ion are respectively

View answer and explanation

Correct option: B

10, 24, 20

Option B (10, 24, 20) is correct because Cesium ion (Cs⁺) has the electronic configuration [Xe], which means it has 10 s-electrons, 24 p-electrons, and 20 d-electrons.

Solution approach

Correct Answer + Core Reason: 10, 24, 20. Cesium ion (Cs⁺) has 10 s-electrons, 24 p-electrons, and 20 d-electrons.

Step-by-Step Solution:

Step 1: Write the electronic configuration of cesium (Cs): 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s¹.

Step 2: Form the cesium ion (Cs⁺) by removing one electron from the outermost shell: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶.

Step 3: Count the number of s, p, and d electrons.\ns-electrons: 1s² 2s² 3s² 4s² 5s² = 2 + 2 + 2 + 2 + 2 = 10\np-electrons: 2p⁶ 3p⁶ 4p⁶ 5p⁶ = 6 + 6 + 6 + 6 = 24\nd-electrons: 3d¹⁰ 4d¹⁰ = 10 + 10 = 20

Why other options are wrong:
- Option A: 8, 26, 10 is incorrect because the number of s, p, and d electrons are not 8, 26, and 10, respectively.
- Option C: 8, 22, 24 is incorrect because the number of s, p, and d electrons are not 8, 22, and 24, respectively.
- Option D: 12, 20, 22 is incorrect because the number of s, p, and d electrons are not 12, 20, and 22, respectively.

Key Concepts:
- Electronic configuration
- s, p, and d electrons

Memory Aids:
- Remember the order of filling orbitals: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, etc.

Quick Tips:
- Always write the complete electronic configuration to accurately count the number of s, p, and d electrons.

156 Easy

156 of 176Question permalink

Remembering +4 | -1

Which of the following is the correct form of Schrodinger wave equation?

View answer and explanation

Correct option: B

\frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {x^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {y^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {z^2}}} + \frac{{8{\mathrm{\pi }^2}\mathrm{m}}}{{{h^2}}}\left( {E - V} \right)\mathrm{\Psi } = 0

Option B (

\frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {x^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {y^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {z^2}}} + \frac{{8{\mathrm{\pi }^2}\mathrm{m}}}{{{h^2}}}\left( {E - V} \right)\mathrm{\Psi } = 0

) is correct because it represents the time-independent Schrödinger equation in three dimensions.

Solution approach

Correct Answer + Core Reason: $\frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {x^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {y^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {z^2}}} + \frac{{8{\mathrm{\pi }^2}\mathrm{m}}}{{{h^2}}}\left( {E - V} \right)\mathrm{\Psi } = 0$ . This is the correct form of the time-independent Schrödinger equation.

Step-by-Step Solution:

Step 1: Recall the time-independent Schrödinger equation in three dimensions:
$\frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {x^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {y^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {z^2}}} + \frac{{8{\mathrm{\pi }^2}\mathrm{m}}}{{{h^2}}}\left( {E - V} \right)\mathrm{\Psi } = 0$ \nwhere:
- $\Psi$ is the wave function
- m is the mass of the particle
- h is Planck's constant
- E is the total energy
- V is the potential energy

Step 2: Compare the given options with the correct equation.

Step 3: Option B matches the correct equation.

Why other options are wrong:
- Option A: $\frac{{{\partial ^2}\mathrm{\Psi }}}{{{\partial ^2}x}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{{\partial ^2}y}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{{\partial ^2}z}} + \frac{{8{\mathrm{\pi }^2}m}}{{{h^2}}}\left( {E - V} \right)\mathrm{\Psi } = 0$ : This option has incorrect notation for the partial derivatives.
- Option C: $\frac{{\partial {\mathrm{\Psi }^2}}}{{\partial {x^2}}} + \frac{{\partial {\mathrm{\Psi }^2}}}{{\partial {y^2}}} + \frac{{\partial {\mathrm{\Psi }^2}}}{{\partial {z^2}}} + \frac{{8{\mathrm{\pi }^2}\mathrm{m}}}{{{h^2}}}\left( {E - V} \right)\mathrm{\Psi } = 0$ : This option has the square of the wave function in the derivative terms, which is incorrect.
- Option D: $\frac{{{\partial ^2}\mathrm{\Psi }}}{{\mathrm{d}{x^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {y^2}}} + \frac{{{\partial ^2}\mathrm{\Psi }}}{{\partial {z^2}}} + \frac{{8{\mathrm{\pi }^2}{\mathrm{m}^2}}}{{{h^2}}}\left( {E - V} \right)\mathrm{\Psi } = 0$ : This option has an incorrect mass term (m²) and uses 'd' instead of ' $\partial$ ' for partial derivatives in the first term.

Key Concepts:
- Schrödinger wave equation
- Time-independent Schrödinger equation
- Wave function ( $\Psi$ )
- Potential energy (V)
- Total energy (E)

Memory Aids:
- Remember the general form of the Schrödinger equation.

Quick Tips:
- Pay attention to the notation and the terms in the Schrödinger equation.

157 Easy

157 of 176Question permalink

Remembering +4 | -1

Which of the following is Heisenberg uncertainty principle?

View answer and explanation

Correct option: A

\Delta x.\Delta p \ge \frac{h}{{4\mathrm{\pi }}}

Option A (

\Delta x.\Delta p \ge \frac{h}{{{{4\mathrm{\pi }}}}}

) is correct because it represents the mathematical expression of Heisenberg's uncertainty principle, stating that the product of the uncertainties in position and momentum must be greater than or equal to

\frac{h}{{{{4{\pi }}}}}

.

Solution approach

Correct Answer + Core Reason: $\Delta x.\Delta p \ge \frac{h}{{{{4\mathrm{\pi }}}}}}$ . This is the correct mathematical expression of Heisenberg's uncertainty principle.

Step-by-Step Solution:

Step 1: The question asks for the correct expression of Heisenberg's uncertainty principle.

Step 2: Recall Heisenberg's uncertainty principle: It states that it is impossible to simultaneously know the exact position and momentum of a particle.

Step 3: The mathematical expression is: $\Delta x.\Delta p \ge \frac{h}{{{{4\pi}}}}$ , where:
- $\Delta x$ is the uncertainty in position.
- $\Delta p$ is the uncertainty in momentum.
- $h$ is Planck's constant.

Step 4: Identify the correct expression from the options.

Why other options are wrong:
- **Option B ( $\Delta x.\Delta p = \frac{h}{{{{4\mathrm{\pi }}}}}$ ): This is incorrect. The uncertainty principle states that the product is greater than or equal to, not equal to.
- Option C ( $\Delta x.\Delta p \le \frac{h}{{{{4\mathrm{\pi }}}}}$ ): This is incorrect. The uncertainty principle states that the product is greater than or equal to, not less than or equal to.
- Option D ( $\Delta x.\Delta p < \frac{h}{{{{4\mathrm{\pi }}}}}$ ): This is incorrect. The uncertainty principle states that the product is greater than or equal to, not less than.

Key Concepts:
- Heisenberg's uncertainty principle
- Uncertainty in position
- Uncertainty in momentum
- Planck's constant

Memory Aids:**
- Remember the inequality sign: $\ge$ (greater than or equal to).

Quick Tips:
- Pay attention to the inequality sign in the expression.

158 Easy

158 of 176Question permalink

Remembering +4 | -1

The number of waves in an orbit are

View answer and explanation

Correct option: B

n

Option B (

n

) is correct because the number of waves in an orbit is equal to the principal quantum number

n

.

Solution approach

Correct Answer + Core Reason: $n$ . The number of waves in an orbit is equal to the principal quantum number.

Step-by-Step Solution:

Step 1: The question asks for the number of waves in an orbit.

Step 2: According to Bohr's model and de Broglie's hypothesis, the circumference of an electron's orbit is an integer multiple of the electron's wavelength: $2\pi r = n\lambda$ , where $n$ is the principal quantum number.

Step 3: This means there are $n$ complete waves in the orbit.

Step 4: Therefore, the number of waves in an orbit is $n$ .

Why other options are wrong:
- **Option A ( $n^2$ ):** This is incorrect. $n^2$ is related to the number of orbitals in a shell, not the number of waves in an orbit.
- **Option C ( $n - 1$ ):** This is incorrect. There's no direct relationship between the number of waves and $n-1$ .
- **Option D ( $n - 2$ ):** This is incorrect. There's no direct relationship between the number of waves and $n-2$ .

Key Concepts:
- Bohr's model
- de Broglie's hypothesis
- Principal quantum number

Memory Aids:
- Remember that the number of waves in an orbit directly corresponds to the principal quantum number, $n$ .

Quick Tips:
- Recall the relationship $2\pi r = n\lambda$ to understand the connection between the orbit's circumference and the electron's wavelength.

159 Easy

159 of 176Question permalink

Understanding +4 | -1

A quanta will have more energy, if :

View answer and explanation

Correct option: B

The frequency is higher

Option B (The frequency is higher) is correct because the energy of a quantum (photon) is directly proportional to its frequency, as described by the equation E = hf.

Solution approach

Correct Answer + Core Reason: The frequency is higher. Energy of a quanta is directly proportional to frequency.

Step-by-Step Solution:

Step 1: Recall the relationship between energy and frequency of a quantum (photon): $E = hf$ , where E is energy, h is Planck's constant, and f is frequency.

Step 2: From the equation, it is clear that energy is directly proportional to frequency.

Why other options are wrong:
- Option A (The wavelength is larger): Energy is inversely proportional to wavelength, not directly proportional.
- Option C (The amplitude is higher): Amplitude is related to the intensity of the light, not the energy of a single quantum.
- Option D (The velocity is lower): The velocity of light (and thus a photon) is constant in a given medium.

Key Concepts:
- Energy of a photon: $E = hf$
- Relationship between energy, frequency, and wavelength

Memory Aids:
- Remember the formula $E = hf$ .

Quick Tips:
- Know the relationship between energy and frequency.

160 Easy

160 of 176Question permalink

Understanding +4 | -1

The number of neutrons present in

{\mathrm{\;}_{19}}{\mathrm{K}^{39}}

is

View answer and explanation

Correct option: C

20

Option C (20) is correct because the number of neutrons is calculated by subtracting the atomic number (number of protons) from the mass number: 39 - 19 = 20.

Solution approach

Correct Answer + Core Reason: 20. Number of neutrons = Mass number - Atomic number.

Step-by-Step Solution:

Step 1: Identify the atomic number and mass number of ${\mathrm{\;}_{19}}{\mathrm{K}^{39}}$ .
- Atomic number (number of protons) = 19.
- Mass number = 39.

Step 2: Calculate the number of neutrons.
- Number of neutrons = Mass number - Atomic number = 39 - 19 = 20.

Why other options are wrong:
- Option A: 39 is the mass number, not the number of neutrons.
- Option B: 19 is the atomic number (number of protons), not the number of neutrons.
- Option D: The number of neutrons is 20, so this option is incorrect.

Key Concepts:
- Atomic number
- Mass number
- Number of neutrons

Memory Aids:
- Number of neutrons = Mass number - Atomic number

Quick Tips:
- Remember the relationship between atomic number, mass number, and number of neutrons.

161 Easy

161 of 176Question permalink

Understanding +4 | -1

An electron from one Bohr stationary orbit can go to next higher orbit

View answer and explanation

Correct option: C

By absorption of electromagnetic radiation of particular frequency

Option C (By absorption of electromagnetic radiation of particular frequency) is correct because an electron transitions to a higher energy level by absorbing a photon with energy equal to the energy difference between the orbits.

Solution approach

Correct Answer + Core Reason: By absorption of electromagnetic radiation of particular frequency. Electrons absorb specific frequencies to jump to higher energy levels.

Step-by-Step Solution:

Step 1: State Bohr's postulate regarding electron transitions.

Step 2: Bohr's postulate states that an electron can transition from one stationary orbit to another by absorbing or emitting energy in the form of electromagnetic radiation.

Step 3: The energy of the absorbed or emitted radiation must be equal to the energy difference between the two orbits: $\Delta E = h\nu$ , where h is Planck's constant and $\nu$ is the frequency of the radiation.

Why other options are wrong:
- Option A: By emission of electromagnetic radiation. Emission occurs when an electron goes to a lower energy level.
- Option B: By absorption of any electromagnetic radiation. The radiation must have a specific frequency corresponding to the energy difference between the orbits.
- Option D: Without emission or absorption of electromagnetic radiation. Energy is always involved in electron transitions.

Key Concepts:
- Bohr's Postulates
- Electron Transitions
- Electromagnetic Radiation

Memory Aids:
- Absorption = Higher energy level
- Emission = Lower energy level

Quick Tips:
- Remember that electron transitions involve specific frequencies of electromagnetic radiation.

162 Easy

162 of 176Question permalink

Remembering +4 | -1

Particle having mass 200 times that of an electron is:

View answer and explanation

Correct option: C

Meson

Option C is correct because a meson has a mass approximately 200 times that of an electron.

Solution approach

Correct Answer + Core Reason: Meson. Mesons have a mass between that of an electron and a proton, approximately 200 times the mass of an electron.

Step-by-Step Solution:

Step 1: Recall the masses of different particles.

Step 2: Compare the given options with the mass of an electron.

Step 3: A meson has a mass approximately 200 times that of an electron.

Why other options are wrong:
- Option A: Proton is much heavier than 200 times the mass of an electron.
- Option B: Positron has the same mass as an electron.
- Option D: Neutron is much heavier than 200 times the mass of an electron.

Key Concepts:
- Elementary particles
- Mass of particles

Memory Aids:
- Meson mass is between electron and proton.

Quick Tips:
- Remember the relative masses of elementary particles.

163 Easy

163 of 176Question permalink

Application +4 | -1

The species having more electrons than neutrons is:

View answer and explanation

Correct option: C

{O^{2 - }}

Option C (

{O^{2 - }}

) is correct because it has 10 electrons and 8 neutrons, thus having more electrons than neutrons.

Solution approach

Correct Answer + Core Reason: ${O^{2 - }}$ . It has 10 electrons and 8 neutrons.

Step-by-Step Solution:

Step 1: Determine the number of electrons and neutrons for each species:
- F: 9 electrons, 10 neutrons
- $Na^+$ : 10 electrons, 12 neutrons
- $O^{2-}$ : 10 electrons, 8 neutrons
- $Mg^{2+}$ : 10 electrons, 12 neutrons

Step 2: Compare the number of electrons and neutrons for each species.

Step 3: $O^{2-}$ has 10 electrons and 8 neutrons, so it has more electrons than neutrons.

Why other options are wrong:
- Option A: F has 9 electrons and 10 neutrons, so it has more neutrons than electrons.
- Option B: $Na^+$ has 10 electrons and 12 neutrons, so it has more neutrons than electrons.
- Option D: $Mg^{2+}$ has 10 electrons and 12 neutrons, so it has more neutrons than electrons.

Key Concepts:
- Number of electrons, protons, and neutrons in atoms and ions.

Memory Aids:
- Remember to account for the charge when determining the number of electrons in an ion.

Quick Tips:
- Number of neutrons = Mass number - Atomic number.

164 Easy

164 of 176Question permalink

Remembering +4 | -1

Photoelectric effect was discovered by :

View answer and explanation

Correct option: D

Hertz

Option D (Hertz) is correct because Heinrich Hertz first observed the photoelectric effect in 1887.

Solution approach

Correct Answer + Core Reason: Hertz. Heinrich Hertz discovered the photoelectric effect.

Step-by-Step Solution:

Step 1: Historical Context: The photoelectric effect was first observed by Heinrich Hertz in 1887 during experiments with radio waves.

Step 2: Hertz's Observation: Hertz noticed that when ultraviolet light shone on metal electrodes, it became easier for sparks to jump across the gap between the electrodes. This observation led to the discovery of the photoelectric effect.

Why other options are wrong:
- Option A: Hallwach. Wilhelm Hallwachs further investigated the photoelectric effect after Hertz's initial observation.
- Option B: Lenard. Philipp Lenard also conducted experiments on the photoelectric effect and observed that the energy of the emitted electrons was independent of the intensity of the light.
- Option C: Einstein. Albert Einstein provided the theoretical explanation of the photoelectric effect in 1905, for which he received the Nobel Prize. However, he did not discover the effect itself.

Key Concepts:
- Photoelectric effect
- History of physics

Memory Aids:
- Hertz = First observation of the photoelectric effect.

Quick Tips:
- Remember that Hertz observed the effect, while Einstein explained it.

165 Easy

165 of 176Question permalink

Application +4 | -1

Which one of the following ions is not isoelectronic with

{\mathrm{O}^{2 - }}?

View answer and explanation

Correct option: A

T{i^ + }

Option A (

T{i^ + }

) is correct because it has 21 electrons, while

{\mathrm{O}^{2 - }}

has 10 electrons. Isoelectronic species have the same number of electrons.

Solution approach

Correct Answer + Core Reason: $T{i^ + }$ . It has 21 electrons, while ${\mathrm{O}^{2 - }}$ has 10.

Step-by-Step Solution:

Step 1: Determine the number of electrons in ${\mathrm{O}^{2 - }}$ . Oxygen (O) has 8 electrons. The 2- charge indicates that it has gained 2 electrons. Therefore, ${\mathrm{O}^{2 - }}$ has 8 + 2 = 10 electrons.

Step 2: Determine the number of electrons in each of the other ions:
- $T{i^ + }$ : Titanium (Ti) has 22 electrons. The +1 charge indicates that it has lost 1 electron. Therefore, $T{i^ + }$ has 22 - 1 = 21 electrons.
- $\mathrm{N}{\mathrm{a}^ + }$ : Sodium (Na) has 11 electrons. The +1 charge indicates that it has lost 1 electron. Therefore, $\mathrm{N}{\mathrm{a}^ + }$ has 11 - 1 = 10 electrons.
- ${\mathrm{F}^ - }$ : Fluorine (F) has 9 electrons. The -1 charge indicates that it has gained 1 electron. Therefore, ${\mathrm{F}^ - }$ has 9 + 1 = 10 electrons.
- ${\mathrm{N}^{3 - }}$ : Nitrogen (N) has 7 electrons. The -3 charge indicates that it has gained 3 electrons. Therefore, ${\mathrm{N}^{3 - }}$ has 7 + 3 = 10 electrons.

Step 3: Identify the ion that does not have 10 electrons. $T{i^ + }$ has 21 electrons, so it is not isoelectronic with ${\mathrm{O}^{2 - }}$ .

Why other options are wrong:
- Option B: $\mathrm{N}{\mathrm{a}^ + }$ is isoelectronic with ${\mathrm{O}^{2 - }}$ .
- Option C: ${\mathrm{F}^ - }$ is isoelectronic with ${\mathrm{O}^{2 - }}$ .
- Option D: ${\mathrm{N}^{3 - }}$ is isoelectronic with ${\mathrm{O}^{2 - }}$ .

Key Concepts:
- Isoelectronic species
- Number of electrons in ions

Memory Aids:
- Isoelectronic: same number of electrons.

Quick Tips:
- Remember to account for the charge when determining the number of electrons in an ion.

166 Easy

166 of 176Question permalink

Remembering +4 | -1

The principal quantum number n can have integral values ranging from:

View answer and explanation

Correct option: B

1\mathrm{\;to\;}\infty

Option B is correct because the principal quantum number n can have integer values starting from 1 and extending to infinity.

Solution approach

Correct Answer + Core Reason: $1\mathrm{\;to\;}\infty$ . The principal quantum number n can have integral values ranging from 1 to infinity.

Step-by-Step Solution:

Step 1: Recall the definition of the principal quantum number (n).
- The principal quantum number (n) determines the energy level or shell of an electron in an atom. It can only have positive integer values.

Step 2: Determine the possible values of n.
- The smallest possible value for n is 1 (corresponding to the innermost shell). There is no upper limit to the value of n; it can theoretically extend to infinity.

Why other options are wrong:
- Option A: 0 is not a valid value for n. n must be a positive integer starting from 1.
- Option C: n cannot be equal to l. l ranges from 0 to n-1.
- Option D: There is no upper limit of 50 for n. n can go to infinity.

Key Concepts:
- Principal quantum number (n)
- Energy levels or shells

Memory Aids:
- Remember that n starts from 1 and goes to infinity.

Quick Tips:
- The principal quantum number defines the energy level of an electron.

167 Easy

167 of 176Question permalink

Remembering +4 | -1

Isotopes have

View answer and explanation

Correct option: D

Different mass number

Option D (Different mass number) is correct because isotopes of an element have the same number of protons but different numbers of neutrons, leading to different mass numbers.

Solution approach

Correct Answer + Core Reason: Different mass number. Isotopes have the same number of protons but different numbers of neutrons, hence different mass numbers.

Step-by-Step Solution:

Step 1: Define isotopes.\nIsotopes are atoms of the same element (same number of protons) that have different numbers of neutrons.

Step 2: Relate neutron number to mass number.\nThe mass number is the sum of protons and neutrons in the nucleus of an atom.

Step 3: Explain why isotopes have different mass numbers.\nSince isotopes have the same number of protons but different numbers of neutrons, their mass numbers will be different.

Why other options are wrong:
- Option A: Different number of protons. This is incorrect because isotopes of the same element have the same number of protons. If they had different numbers of protons, they would be different elements.
- Option B: Same number of neutrons. This is incorrect because isotopes, by definition, have different numbers of neutrons.
- Option C: Different number of electrons. This is incorrect because isotopes are neutral atoms of the same element, so they have the same number of electrons as protons.

Key Concepts:
- Isotopes
- Atomic number (number of protons)
- Mass number (number of protons + number of neutrons)

Memory Aids:
- Isotopes are "identical in position" on the periodic table (same atomic number).

Quick Tips:
- Remember that the number of protons defines the element.

168 Easy

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Analyzing +4 | -1

The electronic configuration

1{s^2},2{s^2}2{p^6},3{s^1}3{p^1}

correctly describes:

View answer and explanation

Correct option: C

Excited state of Mg

Option C (Excited state of Mg) is correct because the ground state configuration of Mg is

1s^22s^22p^63s^2

, and the given configuration shows one electron promoted from 3s to 3p.

Solution approach

Correct Answer + Core Reason: Excited state of Mg. The electronic configuration represents an excited state of Magnesium because one electron has been promoted from the 3s orbital to the 3p orbital.

Step-by-Step Solution:

Step 1: Determine the ground state electronic configuration of each species.\nNa (Z=11): $1s^2 2s^2 2p^6 3s^1$ \nSi+ (Z=13-1=12): $1s^2 2s^2 2p^6 3s^2$ \nMg (Z=12): $1s^2 2s^2 2p^6 3s^2$ \nAl3+ (Z=13-3=10): $1s^2 2s^2 2p^6$

Step 2: Compare the given electronic configuration with the ground state configurations.\nThe given configuration is $1s^2 2s^2 2p^6 3s^1 3p^1$ .

Step 3: Analyze the differences.
- For Na, the ground state configuration is $1s^2 2s^2 2p^6 3s^1$ , which is different from the given configuration.
- For Si+, the ground state configuration is $1s^2 2s^2 2p^6 3s^2$ , which is different from the given configuration.
- For Mg, the ground state configuration is $1s^2 2s^2 2p^6 3s^2$ . The given configuration can be obtained by exciting one electron from the 3s orbital to the 3p orbital. Thus, it is an excited state of Mg.
- For Al3+, the ground state configuration is $1s^2 2s^2 2p^6$ , which is different from the given configuration.

Why other options are wrong:
- Option A: Ground state of Na: The given configuration is not the ground state configuration of Na.
- Option B: Ground state of $\mathrm{S}{\mathrm{i}^ + }$ : The given configuration is not the ground state configuration of Si+.
- Option D: Excited state of $\mathrm{A}{\mathrm{l}^{3 + }}$ : The given configuration is not an excited state of Al3+.

Key Concepts:
- Electronic configuration
- Ground state vs. excited state

Memory Aids:
- Remember the Aufbau principle for filling electrons in orbitals.

Quick Tips:
- Write the ground state electronic configuration first.
- Compare the given configuration with the ground state configuration.

169 Easy

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Application +4 | -1

The energy of an electron in Bohr's orbit of hydrogen atom is

-13.6 \mathrm{~eV}

. The total electronic energy of a hypothetical

\mathrm{He}

atom in which there are no electron-electron repulsions or interactions is

View answer and explanation

Correct option: C

-108.8 \mathrm{~eV}

The correct answer is C (-108.8 eV) because the total electronic energy is calculated by multiplying the energy of a hydrogen-like atom by

Z^2

and then by the number of electrons.

Solution approach

Correct Answer + Core Reason: $-108.8 \mathrm{~eV}$ . The total electronic energy is calculated by considering the energy of each electron in the He atom.

Step-by-Step Solution:

Step 1: Identify the given information: Energy of electron in Bohr's orbit of hydrogen atom = -13.6 eV, He atom has 2 electrons, Atomic number of He (Z) = 2.

Step 2: Calculate the energy of each electron in the He atom using the formula: $E_n = -13.6 \frac{Z^2}{n^2} \mathrm{~eV}$

Step 3: Since there are no electron-electron repulsions, each electron can be treated independently. For the first electron (n=1): $E_1 = -13.6 \frac{2^2}{1^2} = -13.6 \times 4 = -54.4 \mathrm{~eV}$

Step 4: Since both electrons are in the ground state (n=1), the energy of the second electron is also -54.4 eV.

Step 5: Calculate the total electronic energy: $E_{total} = E_1 + E_2 = -54.4 \mathrm{~eV} + (-54.4 \mathrm{~eV}) = -108.8 \mathrm{~eV}$

Why other options are wrong:
- Option A (27.2 eV): This is incorrect. It likely arises from not considering the $Z^2$ factor and the number of electrons correctly.
- Option B (-27.2 eV): This is incorrect. It likely arises from not considering the $Z^2$ factor correctly.
- Option C (-108.8 eV): This is the correct answer, as shown above.
- Option D (108 eV): This is incorrect. The energy should be negative, and the calculation is incorrect.

Key Concepts:
- Bohr's model
- Energy of an electron in a hydrogen-like atom
- Atomic number (Z)

Memory Aids:
- Remember the formula for energy: $E_n = -13.6 \frac{Z^2}{n^2} \mathrm{~eV}$

Quick Tips:
- Remember to account for the atomic number (Z) when calculating the energy of electrons in atoms other than hydrogen.
- Pay attention to the sign of the energy (negative for bound electrons).

170 Easy

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Application +4 | -1

The wavelength of shortest wavelength transition in Lyman series of atomic Hydrogen is

View answer and explanation

Correct option: D

911.9\,{A^ \circ }

Option D (

911.9\,{A^ \circ }

) is correct because it represents the shortest wavelength (highest energy) transition in the Lyman series, corresponding to the transition from infinity to the ground state (n=1).

Solution approach

Correct Answer + Core Reason: $911.9\,{A^ \circ }$ . The shortest wavelength in the Lyman series corresponds to the transition from n = infinity to n = 1.

Step-by-Step Solution:

Step 1: Identify the Lyman series. The Lyman series involves transitions to the n=1 energy level.

Step 2: Determine the shortest wavelength transition. The shortest wavelength corresponds to the largest energy difference, which occurs when an electron transitions from n = infinity to n = 1.

Step 3: Use the Rydberg formula for wavelength: $\frac{1}{\lambda} = R_H (\frac{1}{n_1^2} - \frac{1}{n_2^2})$ , where $R_H$ is the Rydberg constant ( $1.097 \times 10^7 m^{-1}$ ), $n_1 = 1$ (Lyman series), and $n_2 = \infty$ .

Step 4: Substitute the values: $\frac{1}{\lambda} = 1.097 \times 10^7 (\frac{1}{1^2} - \frac{1}{\infty^2}) = 1.097 \times 10^7 (1 - 0) = 1.097 \times 10^7 m^{-1}$ .

Step 5: Calculate the wavelength: $\lambda = \frac{1}{1.097 \times 10^7} m = 9.1157 \times 10^{-8} m$ .

Step 6: Convert meters to Angstroms: $\lambda = 9.1157 \times 10^{-8} m \times \frac{10^{10} {A^ \circ }}{1 m} = 911.57 {A^ \circ } \approx 911.9 {A^ \circ }$ .

Why other options are wrong:
- **Option A ( $1002.7\,{A^ \circ }$ ): This wavelength is longer than the shortest wavelength in the Lyman series. It might correspond to a transition from a lower energy level (e.g., n=3 to n=1), but not the limit.
- Option B ( $1215.67\,{A^ \circ }$ ): This is the wavelength for the transition from n=2 to n=1 in the Lyman series, which is the first line, not the series limit (shortest wavelength).
- Option C ( $1127.3\,{A^ \circ }$ ): This wavelength is also longer than the shortest wavelength in the Lyman series and does not correspond to any specific transition.

Key Concepts:
- Lyman series
- Rydberg formula
- Atomic spectra
- Wavelength and energy relationship

Memory Aids:
- Lyman: Transitions to n=1
- Balmer: Transitions to n=2
- Paschen: Transitions to n=3

Quick Tips:**
- The shortest wavelength in a series corresponds to the transition from n = infinity to the lowest energy level of that series.
- Remember the Rydberg formula and Rydberg constant.

171 Easy

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Analyzing +4 | -1

The atomic number of the element having maximum number of unpaired 3p-electrons is:

View answer and explanation

Correct option: A

15

Option A (15) is correct because the element with atomic number 15 (Phosphorus) has the electronic configuration [Ne] 3s² 3p³, resulting in three unpaired 3p electrons, which is the maximum possible.

Solution approach

Correct Answer + Core Reason: 15. The element with atomic number 15 (Phosphorus) has the maximum number of unpaired 3p electrons.

Step-by-Step Solution:

Step 1: Write the electronic configuration for each element based on their atomic number.
- Atomic number 15 (Phosphorus): $1s^2 2s^2 2p^6 3s^2 3p^3$
- Atomic number 10 (Neon): $1s^2 2s^2 2p^6$
- Atomic number 12 (Magnesium): $1s^2 2s^2 2p^6 3s^2$
- Atomic number 8 (Oxygen): $1s^2 2s^2 2p^4$

Step 2: Determine the number of unpaired 3p electrons for each element.
- Phosphorus: The 3p subshell has 3 electrons. According to Hund's rule, each electron will occupy a separate orbital before pairing occurs. Therefore, there are 3 unpaired 3p electrons.
- Neon: Neon does not have any 3p electrons.
- Magnesium: Magnesium does not have any 3p electrons.
- Oxygen: The 2p subshell has 4 electrons. Two orbitals will have one electron each, and one orbital will have two electrons. Therefore, there are 2 unpaired 2p electrons, but no 3p electrons.

Step 3: Identify the element with the maximum number of unpaired 3p electrons.\nPhosphorus has the maximum number of unpaired 3p electrons (3).

Why other options are wrong:
- Option B: 10: Neon has no 3p electrons.
- Option C: 12: Magnesium has no 3p electrons.
- Option D: 8: Oxygen has 2 unpaired 2p electrons, but no 3p electrons.

Key Concepts:
- Electronic configuration
- Hund's rule
- Unpaired electrons

Memory Aids:
- Remember Hund's rule: electrons will individually occupy each orbital within a subshell before pairing.

Quick Tips:
- Write the electronic configuration first.
- Apply Hund's rule to determine the number of unpaired electrons.

172 Easy

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Application +4 | -1

The electron in the hydrogen atom is excited to the 4th orbit. Number of spectral lines expected in the emission is

View answer and explanation

Correct option: B

6

Option B (6) is correct because the number of spectral lines is calculated using the formula n(n-1)/2 where n is the orbit number.

Solution approach

Correct Answer + Core Reason: 6. The number of spectral lines is calculated using the formula n(n-1)/2.

Step-by-Step Solution:

Step 1: Identify the initial and final energy levels: The electron transitions from the 4th orbit (n = 4) to lower energy levels.

Step 2: Use the formula for the number of spectral lines: The number of spectral lines is given by $\frac{{n(n - 1)}}{2}$ , where $n$ is the initial energy level. In this case, $n = 4$ , so the number of spectral lines is $\frac{{4(4 - 1)}}{2} = \frac{{4 \times 3}}{2} = 6$ .

Step 3: Final Answer: 6

Why other options are wrong:
- Option A: 4: Incorrect, this is not the correct number of spectral lines.
- Option C: 10: Incorrect, this is not the correct number of spectral lines.
- Option D: 12: Incorrect, this is not the correct number of spectral lines.

Key Concepts:
- Hydrogen spectrum
- Spectral lines
- Electronic transitions

Memory Aids:
- Number of spectral lines: $\frac{{n(n - 1)}}{2}$

Quick Tips:
- Remember the formula for calculating the number of spectral lines when an electron transitions from a higher energy level to a lower energy level.

173 Easy

173 of 176Question permalink

Understanding +4 | -1

Which relates to light only as stream of particles?

View answer and explanation

Correct option: B

Photoelectronic effect

Option B (Photoelectronic effect) is correct because the photoelectric effect demonstrates the particle nature of light (photons) interacting with electrons.

Solution approach

Correct Answer + Core Reason: Photoelectronic effect. The photoelectric effect demonstrates the particle nature of light.

Step-by-Step Solution:

Step 1: Define the photoelectric effect: The emission of electrons when light shines on a material.

Step 2: Explain why it supports the particle nature of light: The photoelectric effect can only be explained if light is composed of discrete packets of energy (photons) that transfer their energy to electrons.

Step 3: Key Concept: Light as particles (photons) can eject electrons from a metal surface if the photon energy is greater than the work function of the metal.

Step 4: Final Answer: Photoelectronic effect

Why other options are wrong:
- Option A: Diffraction: Diffraction demonstrates the wave nature of light, as it involves the bending of light waves around obstacles.
- Option C: Interference: Interference also demonstrates the wave nature of light, as it involves the superposition of light waves to create constructive or destructive patterns.
- Option D: Planck’s theory: Planck's theory introduced the concept of quantized energy, but it doesn't exclusively relate to the particle nature of light. It laid the foundation for both wave and particle duality.

Key Concepts:
- Photoelectric effect
- Particle nature of light
- Wave-particle duality

Memory Aids:
- Photoelectric effect = Photons ejecting electrons

Quick Tips:
- Remember that the photoelectric effect is a key piece of evidence for the particle nature of light.

174 Easy

174 of 176Question permalink

Remembering +4 | -1

Compared to the mass of lightest nuclei, the mass of an electron is only (app.)

View answer and explanation

Correct option: C

\frac{1}{{1800}}

Option C (

\frac{1}{{1800}}

) is correct because the mass of an electron is approximately 1/1836th of the mass of a proton (or a neutron), which are the lightest nuclei.

Solution approach

Correct Answer + Core Reason: $\frac{1}{{1800}}$ . The mass of an electron is approximately 1/1836th of the mass of a proton.

Step-by-Step Solution:

Step 1: Recall the approximate mass of an electron and the mass of a proton (or neutron).

Step 2: The mass of an electron is approximately $9.1 \times 10^{-31}$ kg.

Step 3: The mass of a proton is approximately $1.67 \times 10^{-27}$ kg.

Step 4: Calculate the ratio of the mass of an electron to the mass of a proton: $\frac{9.1 \times 10^{-31}}{1.67 \times 10^{-27}} \approx \frac{1}{1836}$ .

Step 5: Approximate the ratio to the closest option.

Why other options are wrong:
- **Option A ( $\frac{1}{{80}}$ ): This is a much larger fraction and not close to the actual ratio.
- Option B ( $\frac{1}{{800}}$ ): This is also a larger fraction than the actual ratio.
- Option D ( $\frac{1}{{2800}}$ ): This is a smaller fraction than the actual ratio.

Key Concepts:
- Mass of an electron
- Mass of a proton (or neutron)

Memory Aids:
- Remember that the mass of an electron is much smaller than the mass of a proton or neutron.

Quick Tips:**
- Know the approximate mass of an electron and a proton.

175 Easy

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Analyzing +4 | -1

Consider the species

\mathrm{CH}_4, \mathrm{NH}_4^{+}

and

\mathrm{BH}_4^{-}

. Choose the correct option with respect to these species.

View answer and explanation

Correct option: B

They are isoelectronic and all have tetrahedral structures.

Option B (They are isoelectronic and all have tetrahedral structures) is correct because all three species have 8 valence electrons and four bond pairs, resulting in a tetrahedral geometry.

Solution approach

Correct Answer + Core Reason: They are isoelectronic and all have tetrahedral structures.

Step-by-Step Solution:

Step 1: Determine if the species are isoelectronic.
$CH_4$ : C has 4 valence electrons + 4 H = 4 + 4 = 8 electrons
$NH_4^+$ : N has 5 valence electrons + 4 H - 1 (positive charge) = 5 + 4 - 1 = 8 electrons
$BH_4^-$ : B has 3 valence electrons + 4 H + 1 (negative charge) = 3 + 4 + 1 = 8 electrons\nAll three species have 8 valence electrons, so they are isoelectronic.

Step 2: Determine the structure of each species.
$CH_4$ : Carbon has 4 bond pairs and 0 lone pairs. Tetrahedral.
$NH_4^+$ : Nitrogen has 4 bond pairs and 0 lone pairs. Tetrahedral.
$BH_4^-$ : Boron has 4 bond pairs and 0 lone pairs. Tetrahedral.\nAll three species have tetrahedral structures.

Step 3: Conclusion: They are isoelectronic and all have tetrahedral structures.

Why other options are wrong:
- Option A: All three have tetrahedral structures, not just two.
- Option C: All three are isoelectronic, not just two.
- Option D: All three are isoelectronic and have tetrahedral structures.

Key Concepts:
- Isoelectronic species
- Tetrahedral structure
- Valence electrons
- VSEPR theory

Memory Aids:
- Tetrahedral geometry has 4 bond pairs and 0 lone pairs.

Quick Tips:
- Use VSEPR theory to determine the shape of molecules and ions.

176 Easy

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Application +4 | -1

The total number of valency electrons for

\mathrm{NH}_4^ +

is :

View answer and explanation

Correct option: B

8

Option B (8) is correct because nitrogen has 5 valence electrons, each hydrogen has 1, and the +1 charge means one electron is removed: 5 + (4*1) - 1 = 8.

Solution approach

Correct Answer + Core Reason: 8. The total number of valence electrons in $\mathrm{NH}_4^ +$ is 8.

Step-by-Step Solution:

Step 1: Determine the number of valence electrons for each atom in the $\mathrm{NH}_4^ +$ ion.\nNitrogen (N) is in group 15 (or 5A), so it has 5 valence electrons.\nHydrogen (H) is in group 1 (or 1A), so it has 1 valence electron.

Step 2: Calculate the total number of valence electrons from the atoms:
1 Nitrogen atom: 1 * 5 = 5 valence electrons
4 Hydrogen atoms: 4 * 1 = 4 valence electrons

Step 3: Account for the positive charge. A +1 charge means one electron has been removed from the neutral molecule.

Step 4: Calculate the total number of valence electrons in the ion:\nTotal valence electrons = (Valence electrons from N) + (Valence electrons from H) - (Charge)\nTotal valence electrons = 5 + 4 - 1 = 8

Why other options are wrong:
- Option A: Incorrect. 9 valence electrons would be obtained if the positive charge was not accounted for correctly (5 + 4 = 9).
- Option C: Incorrect. 6 valence electrons is not the correct count for the given molecule.
- Option D: Incorrect. 11 valence electrons is not the correct count for the given molecule.

Key Concepts:
- Valence Electrons
- Lewis Structures
- Ionic Charge

Memory Aids:
- Remember to subtract electrons for positive charges and add electrons for negative charges when calculating valence electrons in ions.

Quick Tips:
- Always account for the charge of the ion when calculating the total number of valence electrons.

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