Given below are two statements. One is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A) :$ The binding energy per nucleon is found to be practically independent of the atomic number $A$,for nuclei with mass numbers between $30$ and $170$.
Reason $(R) :$ Nuclear force is long range.
In the light of the above statements,choose the correct answer from the options given below $:$

• A
  $(A)$ is false but $(R)$ is true
• B
  $(A)$ is true but $(R)$ is false
• C
  Both $(A)$ and $(R)$ are true and $(R)$ is the correct explanation of $(A)$
• D
  Both $(A)$ and $(R)$ are true but $(R)$ is $\text{NOT}$ the correct explanation of $(A)$