The ratio of densities of nuclei with mass numbers A and 2A, respectively is

1 : 1

The correct answer is Option (3) → 1 : 1

Density of a nucleus: $\rho = \frac{\text{Mass}}{\text{Volume}}$

Assuming spherical nucleus, radius $R \propto A^{1/3}$

Volume, $V \propto R^3 \propto A$

Mass, $M \propto A$

So, $\rho = \frac{M}{V} \propto \frac{A}{A} = \text{constant}$

Therefore, the ratio of densities of nuclei with mass numbers $A$ and $2A$ is:

1 : 1