Given below are two statements. One is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: The first ionization enthalpy for oxygen is lower than that of nitrogen.
Reason $R$: The four electrons in $2p$ orbitals of oxygen experience more electron-electron repulsion.
In the light of the above statements,choose the correct answer from the options given below.

• 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 not correct.
• D
  $A$ is not correct but $R$ is correct.