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 of $O$ is lower than that of $N$ and $F$.
Reason $R$: The loss of an electron from $O$ leads to a stable half-filled $p$ orbital.
In light of the above statements, choose the most appropriate 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 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.