The radius $R$ of a nucleus of mass number $A$ can be estimated by the formula $R=\left(1.3 \times 10^{-15}\right) A^{1 / 3} \mathrm{~m}$. It follows that the mass density of a nucleus is of the order of :
$\left(M_{\text {prot. }} \cong M_{\text {neut. }} \simeq 1.67 \times 10^{-27} \mathrm{~kg}\right)$
Correct Option: , 4
(4) Density of nucleus, $\rho=\frac{\text { Mass }}{\text { Volume }}=\frac{m A}{\frac{4}{3} \pi R^{3}}$
$\Rightarrow \rho=\frac{m A}{\frac{4}{3} \pi\left(R_{0} A^{1 / 3}\right)^{3}} \quad\left(\because R=R_{0} A^{1 / 3}\right)$
Here $m=$ mass of a nucleon
$\therefore \rho=\frac{3 \times 1.67 \times 10^{-27}}{4 \times 3.14 \times\left(1.3 \times 10^{-15}\right)^{3}}$ (Given, $R_{0}=1.3 \times 10^{-15}$ )
$\Rightarrow \rho=2.38 \times 10^{17} \mathrm{~kg} / \mathrm{m}^{3}$
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