If the radius of a nucleus with atomic number $Z = 50$ is $9 \times 10^{-15} \ m$,what is the electric potential at its surface?

Which of the following is not made by quarks?

Show that the volume of a nucleus is proportional to its atomic mass number $A$.

Briefly explain the discovery of neutrons and how it can be demonstrated.

Match the following fundamental forces of nature with their relative strength:

List-$I$	List-$II$
$(A)$ Strong nuclear force	$(i)$ $10^{-2}$
$(B)$ Weak nuclear force	(ii) $1$
$(C)$ Electromagnetic force	(iii) $10^{-39}$
$(D)$ Gravitational force	(iv) $10^{-13}$

Nuclei with magic numbers of protons $Z = 2, 8, 20, 28, 50, 82$ and magic numbers of neutrons $N = 2, 8, 20, 28, 50, 82, 126$ are found to be very stable.
$(i)$ Verify this by calculating the proton separation energy $S_p$ for $^{120}Sn$ $(Z = 50)$ and $^{121}Sb$ $(Z = 51)$. The proton separation energy for a nuclide is the minimum energy required to separate the least tightly bound proton from a nucleus of that nuclide. It is given by $S_p = (M_{Z-1, N} + M_H - M_{Z, N})c^2$. Given:
$^{119}In = 118.9058 \ u, ^{120}Sn = 119.902199 \ u, ^{121}Sb = 120.903824 \ u, ^1H = 1.0078252 \ u$
$(ii)$ What does the existence of magic numbers indicate?