Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
**Assertion (A):** The density of the copper (${}^{64}_{29}\text{Cu}$) nucleus is greater than that of the carbon (${}^{12}_{6}\text{C}$) nucleus.
**Reason (R):** The nucleus of mass number A has a radius proportional to $A^{1/3}$.
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer: (B) (A) is not correct but (R) is correct
$R = R_0A^{1/3}$, so the nuclear volume is proportional to $A$, and so is the mass. The density
$$\rho = \frac{Am_n}{\frac43\pi R_0^3A}$$
does not depend on $A$: all nuclei have nearly the same density.
So A is wrong and R is correct.
Solution by Sreeraj P, M.Sc Physics