Given below are two statements $:$ one is labelled as Assertion $(A)$ and other is labelled as Reason $(R).$
Assertion $(A) :$ Neutrons penetrate matter more readily as compared to protons.
Reason $(R) :$ Neutrons are slightly more massive than protons.

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