Assertion $(A)$: $16$th group elements have higher ionisation enthalpy values than $15$th group elements in the corresponding periods.
Reason $(R)$: $15$th group elements have half-filled stable electronic configurations.

• 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.