## 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

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

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) $E_{1}=E_{2}= E_{3}$

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

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

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) $0.1936×10^{-10}ergs$

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) $5.25 × 10^{-28}m$

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) $n=4,l=1,m=1,m_{s}=-\frac{1}{2}$

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

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) $n=3,l=2,m=1,s=+\frac{1}{2}$