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2
MCQ (Single Correct Answer)

The gravitational force between a H -atom and another particle of mass $m$ will be given by Newton's law

$$F=G \frac{M \cdot m}{r^2}, \text { where } r \text { is in } \mathrm{km} \text { and }$$

A
$M=m_{\text {proton }}+m_{\text {electron }}$
B
$M=m_{\text {proton }}+m_{\text {electron }}-\frac{B}{\mathrm{c}^2}(B=13.6 \mathrm{eV})$.
C
$M$ is not relate to the mass of the hydrogen atom.
D
$M=m_{\text {proton }}+m_{\text {electron }}-\frac{|V|}{c^2}(|V|=$ magnitude of the potential energy of electron in the H -atom.
3
MCQ (Single Correct Answer)

When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom

A
do not change for any type of radioactivity
B
change for $\alpha$ and $\beta$-radioactivity but not for $\gamma$-radioactivity
C
change for $\alpha$-radioactivity but not for others
D
change for $\beta$-radioactivity but not for others
4
MCQ (Single Correct Answer)

$M_x$ and $M_y$ denote the atomic masses of the parent and the daughter nuclei respectively in radioactive decay. The $Q$-value for a $\beta^{-}$decay is $Q_1$ and that for a $\beta^{+}$decay is $Q_2$. If $m_e$ denotes the mass of an electron, then which of the following statements is correct?

A
$Q_1=\left(M_x-M_y\right) c^2$ and $Q_2=\left[M_x-M_y-2 m_e\right] c^2$
B
$Q_1=\left(M_x-M_y\right) c^2$ and $Q_2=\left(M_x-M_y\right) c^2$
C
$Q_1=\left(M_x-M_y-2 m_e\right) c^2$ and $Q_2=\left(M_x-M_y+2 c_e\right) c^2$
D
$Q_1=\left(M_x-M_y+2 m_{\mathrm{e}}\right) c^2$ and $Q_2=\left(M_x-m_y+2 m_e\right) c^2$
5
MCQ (Single Correct Answer)

Tritium is an isotope of hydrogen whose nucleus triton contains 2 neutrons and 1 proton. Free neutrons decay into $p+\bar{e}+\bar{n}$. If one of the neutrons in Triton decays, it would transform into $\mathrm{He}^3$ nucleus. This does not happen. This is because

A
Triton energy is than that of a $\mathrm{He}^3$ nucleus
B
The electron created in the beta decay process cannot remain in the nucleus
C
both the neutons in triton have to decay simultaneously resulting in a nucleus with 3 protons, which is not $\mathrm{aHe}^3$ nucleus.
D
free neutrons decay due to external perturbations which is absent in triton nucleus
6
MCQ (Single Correct Answer)

Heavy stable nuclei have more neutrons than protons. This is because of the fact that

A
neutrons are heavier than protons
B
electrostatic force between protons are repulsive
C
neutrons decay into protons through beta decay
D
nuclear forces between neutrons are weaker than that between protons
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