Define mass. Write the unit of mass used in nuclear physics and its value in kilograms.

An atom ${}_3^8 X$ is bombarded by a shower of fundamental particles. In $10 \ s$, this atom absorbs $10$ electrons, $10$ protons, and $9$ neutrons. The percentage growth in the surface area of the nucleus is recorded as: (in $\%$)

$A$ nucleus disintegrates into two nuclear parts,in such a way that the ratio of their nuclear radii is $1: 2^{1/3}$. Their respective speeds have a ratio of $n: 1$. The value of $n$ is $.....$.

Consider the following statements ($X$ and $Y$ stand for two different elements):
$(I)$ ${ }_{32}^{65} X$ and ${ }_{33}^{65} Y$ are isotopes.
$(II)$ ${ }_{42}^{86} X$ and ${ }_{42}^{85} Y$ are isotopes.
$(III)$ ${ }_{85}^{174} X$ and ${ }_{88}^{177} Y$ have the same number of neutrons.
$(IV)$ ${ }_{92}^{235} X$ and ${ }_{94}^{235} Y$ are isobars.
Which of the above statements are correct?

Two protons are kept at a separation of $10 \ nm$. Let $F_n$ and $F_e$ be the nuclear force and the electromagnetic force between them,respectively.

What is the mass number of a nucleus having a radius equal to $\frac{1}{3}$ of that of ${}^{189}\text{Os}$?