Given below are two statements:
Assertion $(A)$: Conductivity of an electrolyte decreases on dilution.
Reason $(R)$: On dilution,the number of ions per unit volume increases.
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 and $(R)$ is not the correct explanation of $(A)$
• C
  $(A)$ is correct but $(R)$ is not correct
• D
  $(A)$ is not correct but $(R)$ is correct