## Atomic Structure Questions and Answers Part-3

1. Which of the following pairs have identical values of e/m?
a) A proton and a neutron
b) A proton and deuterium
c) Deuterium and an $\alpha$ -particle
d) An electron and $\gamma$-rays

Answer: c
Explanation: Deuterium and an $\alpha$ -particle

2. Chlorine exists in two isotopic forms, $C\ell-37 and C\ell-35$     but its atomic mass is 35.5. This indicates the ratio of $C\ell-37 and C\ell-35$    is approximately
a) 1 : 2
b) 1 : 1
c) 1 : 3
d) 3 : 1

Answer: c
Explanation: 1 : 3

3. If $E_{1},E_{2} and E_{3}$   represent respectively the kinetic energies of an electron and an alpha particle and a proton each having same de-broglie wavelength then
a) $E_{1}>E_{3}> E_{2}$
b) $E_{2}>E_{3}> E_{1}$
c) $E_{1}>E_{2}> E_{3}$
d) $E_{1}=E_{2}= E_{3}$

Answer: a
Explanation: $E_{1}>E_{3}> E_{2}$

4. If travelling at same speeds, which of the following matter waves have the shortest wavelength?
a) Electron
b) Alpha particle$\left(He^{2+}\right)$
c) Neutron
d) Proton

Answer: b
Explanation: Alpha particle$\left(He^{2+}\right)$

5. The third line of the Balmer series, in the emission spectrum of the hydrogen atom, is due to the transition from the
a) fourth Bohr orbit to the first Bohr orbit
b) fifth Bohr orbit to the second Bohr orbit
c) sixth Bohr orbit to the third Bohr orbit
d) seventh Bohr orbit to the third Bohr orbit

Answer: b
Explanation: fifth Bohr orbit to the second Bohr orbit

6. In a Bohr model of an atom, when an electron jumps from n = 3 to n = 1, how much energy will be emitted?
a) $2.15 ×10^{-11}ergs$
b) $2.389 ×10^{-12}ergs$
c) $0.239×10^{-10}ergs$
d) $0.1936×10^{-10}ergs$

Answer: d
Explanation: $0.1936×10^{-10}ergs$

7. The uncertainty in the momentum of an electron is $1.0 × 10^{-5}kg ms^{-1}$  . The uncertainty in its position will be $h=\left(6.62 ×10^{-34}kgm^{2}s^{-1}\right)$
a) $1.05 × 10^{-26}m$
b) $1.05 × 10^{-28}m$
c) $5.27 × 10^{-30}m$
d) $5.25 × 10^{-28}m$

Answer: c
Explanation: $5.27 × 10^{-30}m$

8. Which one of the following set of quantum numbers is not possible for 4p electron?
a) $n=4,l=1,m=-1,m_{s}=+\frac{1}{2}$
b) $n=4,l=1,m=0,m_{s}=+\frac{1}{2}$
c) $n=4,l=1,m=2,m_{s}=+\frac{1}{2}$
d) $n=4,l=1,m=1,m_{s}=-\frac{1}{2}$

Answer: c
Explanation: $n=4,l=1,m=2,m_{s}=+\frac{1}{2}$

9. A neutral atom (Atomic No > 1) has
a) electron and proton
b) neutron and electron
c) neutron, electron and proton
d) neutron and proton

Answer: c
Explanation: A neutral atom with Z > 1 can have neutron, proton and electron

10. Which of the following set of quantum numbers belong to highest energy?
a) $n=4,l=0,m=0,s=+\frac{1}{2}$
b) $n=3,l=0,m=0,s=+\frac{1}{2}$
c) $n=3,l=1,m=1,s=+\frac{1}{2}$
d) $n=3,l=2,m=1,s=+\frac{1}{2}$

Answer: d
Explanation: Atomic orbitals are 4s, 3s, 3p and 3d. (n + l) values being 4, 3, 4 and 5. Hence 3d has highest energy.