Given below are two statements:
Assertion $(A)$: Protium and deuterium differ in their rates of reactions.
Reason $(R)$: They have different enthalpies of bond dissociation.
The correct answer is:

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