Explanation

(c) Experimental measurements show that volume of a nucleus is proportional to its mass number$A$. If $R\ $is the radius of the nucleus assumed to be spherical, then its volume
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \left( \frac{4}{3}\pi R^{3} \right)\ \propto A$
or $R\ \propto \ A^{1/3}$
or $\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ R = R_{0}\ A^{1/3}$
where $R_{0}$ is an empirical constant whose value is found to be $1.1\ \times \ 10^{- 15}\ m.$