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) $10^{-13}$

The unit of length convenient on the nuclear scale is a fermi: $1 \; f = 10^{-15} \; m$. Nuclear sizes obey roughly the following empirical relation: $r = r_{0} A^{1/3}$,where $r$ is the radius of the nucleus,$A$ is its mass number,and $r_{0}$ is a constant equal to about $1.2 \; f$. Show that the rule implies that nuclear mass density is nearly constant for different nuclei. Estimate the mass density of a sodium nucleus.

An atom of mass number $15$ and atomic number $7$ captures an $\alpha$-particle and then emits a proton. The mass number and atomic number of the resulting product will respectively be

The atomic masses of two isotopes of an element are $34.98 \ u$ and $36.98 \ u$ and their relative abundances are $75.4 \%$ and $24.6 \%$ respectively. The average atomic mass of the element is: (in $u$)

The value of the average density of a nucleus is $\qquad$ times that of water.

$\pi$ mesons can be