Atoms — DPP 2

20 NEET questions from Atoms, with answers and explanations. Attempt it as a timed test to get scoring, accuracy breakdown and mistake tracking.

Attempt this test free 20 questions · 30 minutes · +80 marks
1
A proton strikes another proton at rest with speed vo. Assume the impact parameter to be zero. Their closest distance of approach is (mass of proton is m)
  1. A $\frac{\mathrm{e}^{2}}{4 \pi \varepsilon \mathrm{mv}_{\mathrm{o}}^{2}}$
  2. B $\frac{\mathrm{e}^{2}}{\pi \varepsilon_{0} \mathrm{mv}_{\mathrm{o}}^{2}}$
  3. C $\frac{\mathrm{e}^{2}}{\mathrm{mv}_{\mathrm{o}}^{2}}$
  4. D Zero
Show answer

Correct answer: B

2
A closest distance of approach of an α particle travelling with a velocity v towards Al$_{13}$ nucleus is d. The closest distance of approach of an alpha particle travelling with velocity 4v towards Fe$_{26}$ nucleus is
  1. A d/2
  2. B d/4
  3. C d/8
  4. D d/16
Show answer

Correct answer: C

3
What is the distance of closest approach when a 5 MeV proton approaches a gold nucleus (Z = 79)?
  1. A $4.13 \times 10 ^ { - 14 } \mathrm {~m}$
  2. B $2.27 \times 10 ^ { - 14 } \mathrm {~m}$
  3. C $3.9 \times 10 ^ { - 14 } \mathrm {~m}$
  4. D $5.6 \times 10 ^ { - 12 } \mathrm {~m}$
Show answer

Correct answer: B

4
Of the various series of the hydrogen spectrum, the one which lies completely in the ultraviolet region is
  1. A Lyman series
  2. B Balmer series
  3. C Paschen series
  4. D Brackett series
Show answer

Correct answer: A

5
The radius of the innermost electron orbit of hydrogen atom is $5.3 \times 10 ^ { - 11 } \mathrm {~m}$. The radius of n = 3 orbit will be:
  1. A $2.12 \AA$
  2. B $5.3 \AA$
  3. C $4.77 \AA$
  4. D $1.59 \AA$
Show answer & explanation

Correct answer: C

$r_{3}=r_{1} \times 3^{2}=9 \times 5.3 \times 10^{-11}=4.77 \AA$
Therefore, option (C) is the correct answer.
6
An alpha particle colliding with one of the electrons in a gold atom loses
  1. A most of its momentum
  2. B about $\frac{1}{3} \mathrm{rd}$ of its momentum
  3. C little of its energy ( $\Delta K \rightarrow 0$ )
  4. D most of its energy
Show answer

Correct answer: C

7
When a hydrogen atom is raised from the ground state to third state
  1. A both kinetic energy and potential energy increases
  2. B both kinetic energy and potential energy decreases
  3. C potential energy increases and kinetic energy decreases
  4. D potential energy decreases and kinetic energy increases
Show answer

Correct answer: C

8
What is the ratio of the shortest wavelength of the Balmer series to the shortest wavelength of the Lyman series?
  1. A 4 : 1
  2. B 4 : 3
  3. C 4 : 9
  4. D 5 : 9
Show answer

Correct answer: A

9
The transition from the state $n = 3$ to $n = 1$ in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from:
  1. A $2 \rightarrow 1$
  2. B $3 \rightarrow 2$
  3. C $4 \rightarrow 3$
  4. D $4 \rightarrow 2$
Show answer & explanation

Correct answer: C

Lyman series produces U.V. radiation. Balmer series produces visible radiation. Pachan series produces Infrared radiation so correct answer is 4 → 3
Therefore, option (C) is the correct answer.
10
If the ionization potential of hydrogen atom is 13.6 eV, its energy in the n = 3 is approximately.
  1. A - 1.14 eV
  2. B - 1.51 eV
  3. C - 3.4 eV
  4. D - 4.53 eV
Show answer

Correct answer: B

11
What will be the angular momentum in fourth orbit, if L is the angular momentum of the electron in the second orbit of hydrogen atom?
  1. A 2L
  2. B $\frac { 3 } { 2 } L$
  3. C $\frac { 2 } { 3 } L$
  4. D $\frac { L } { 2 }$
Show answer & explanation

Correct answer: A

According to Bohr’s model, angular momentum,
$L=\frac{n h}{2 \pi}$ i.e. $\mathrm{L} \propto \mathrm{n}$
∴ angular momentum in 2nd orbit L’ = 2L
Therefore, option (A) is the correct answer.
12
The ground state energy of H-atom is -13.6 eV. The energy needed to ionise H-atom from its second excited state is
  1. A 1.51 eV
  2. B 3.4 eV
  3. C 13.6 eV
  4. D 12.1 eV
Show answer

Correct answer: A

13
Assertion (A): Both the Thomson’s as well as the Rutherford’s models constitute an unstable system.
Reason (R): Thomson’s model is unstable electrostatically while Rutherford’s model is unstable because of the electromagnetic radiation of orbiting electrons.
  1. A Both Assertion (A) and Reason (R) are True and the Reason (R) is a correct explanation of the Assertion (A).
  2. B Both Assertion (A) and Reason (R) are True but Reason (R) is not a correct explanation of the Assertion (A).
  3. C Assertion (A) is True but the Reason (R) is False.
  4. D Assertion (A) and Reason (R) are False
Show answer

Correct answer: A

14
Assertion (A): In Bohr’s atomic model, $\frac{1}{\lambda} \propto z^{2}$
Reason (R): In Bohr’s atomic model E ∝ z$^{2}$
  1. A Both Assertion (A) and Reason (R) are True and the Reason (R) is a correct explanation of the Assertion (A).
  2. B Both Assertion (A) and Reason (R) are True but Reason (R) is not a correct explanation of the Assertion (A).
  3. C Assertion (A) is True but the Reason (R) is False
  4. D Assertion (A) and Reason (R) are False
Show answer

Correct answer: A

15
The angular momentum of an electron in a hydrogen atom is proportional to (where r is radius of orbit)
  1. A $\frac { 1 } { \sqrt { r } }$
  2. B $\frac { 1 } { r }$
  3. C $\sqrt { r }$
  4. D $r ^ { 2 }$
Show answer

Correct answer: C

16
Most of the alpha particles in Rutherford's experiment passed through the gold foil without any deflection. This observation indicates that:
  1. A Atoms are solid
  2. B Atoms have a dense nucleus
  3. C Most of the atom is empty space
  4. D Electrons revolve in circular orbits
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Correct answer: C

17
When an α-particle happens to come near a nucleus the intense electric field scatters it through a large angle then what is the effect of atomic electrons on the α-particle?
  1. A Repel α-particle lightly
  2. B Deviate α-particle from their path
  3. C Due to the electron cloud it blocks the path of α-particle
  4. D Do not appreciably effect
Show answer

Correct answer: D

18
According to Rutherford's model, the nucleus of an atom is:
  1. A Positively charged and very small
  2. B Negatively charged and large
  3. C Neutral and occupies most of the space
  4. D Made up of electrons and neutrons
Show answer

Correct answer: A

19
A particle of mass M at rest decays into two particles of masses $\mathrm { m } _ { 1 }$ and $\mathrm { m } _ { 2 }$, having non-zero velocities. The ratio of the de-Broglie wavelength of the particles, $\lambda _ { 1 } / \lambda _ { 2 }$ is
  1. A $m _ { 1 } / m _ { 2 }$
  2. B $m _ { 2 } / m _ { 1 }$
  3. C 1 : 1
  4. D $\sqrt { m _ { 2 } } / \sqrt { m _ { 1 } }$
Show answer & explanation

Correct answer: C

By law of conservation of momentum,
$\begin{array}{l}0=m_{1} v_{1}+m_{2} v_{2} \\ m_{1} v_{1}=-m_{2} v_{2}\end{array}$
Negative sign indicates that both the particles are moving in opposites directions.
Now, de-Broglie wavelengths,
$\begin{array}{l}\lambda_{1}=\frac{\mathrm{h}}{\mathrm{m}_{1} \mathrm{v}_{1}} \text { and } \lambda_{2}=\frac{\mathrm{h}}{\mathrm{m}_{2} \mathrm{v}_{2}} \\ \therefore \frac{\lambda_{1}}{\lambda_{2}}=\frac{\mathrm{m}_{2} \mathrm{v}_{2}}{\mathrm{~m}_{1} \mathrm{v}_{1}}=1\end{array}$
Therefore, option (C) is the correct answer.
20
Assertion (A): In Bohr’s model of atom angular momentum of electron is not conserved.
Reason (R): In Bohr’s model angular momentum of electron can be zero.
  1. A Both Assertion (A) and Reason (R) are True and the Reason (R) is a correct explanation of the Assertion (A).
  2. B Both Assertion (A) and Reason (R) are True but Reason (R) is not a correct explanation of the Assertion (A).
  3. C Assertion (A) is True but the Reason (R) is False.
  4. D Assertion (A) and Reason (R) are False
Show answer

Correct answer: D

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