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 $\left({ }_{29}^{64} Cu \right)$ nucleus is greater than that of the carbon $\left({ }_6^{12} C \right)$ 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.

• A
  $(A)$ is correct but $(R)$ is not correct
• B
  $(A)$ is not correct but $(R)$ is correct
• C
  Both $(A)$ and $(R)$ are correct and $(R)$ is the correct explanation of $(A)$
• D
  Both $(A)$ and $(R)$ are correct but $(R)$ is not the correct explanation of $(A)$