"On moving left to right,ionization energy increases due to increasing $Z_{eff}$." In which of the following pairs is the above statement $NOT$ $CORRECT$?

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:

Given below are two statements $:$
Statement $(I) :$ The first ionisation enthalpy of group $14$ elements is higher than the corresponding elements of group $13.$
Statement $(II) :$ Melting points and boiling points of group $13$ elements are in general much higher than those of the corresponding elements of group $14.$ In the light of the above statements,choose the most appropriate answer from the options given below $:$

The correct order in which the first ionisation potential increases is

Assertion $(A)$: First ionisation enthalpy of oxygen is less than that of nitrogen.
Reason $(R)$: Atoms with half-filled or completely filled orbitals are less stable.
The correct option among the following is:

Sodium generally does not show an oxidation state of $+2$,because of its