The third ionisation enthalpy is highest in

Which ionisation potential $(IP)$ in the following equations involves the greatest amount of energy?

Outermost electronic configurations of four elements $A, B, C, D$ are given below:
$A: 3s^{2}$
$B: 3s^{2} 3p^{1}$
$C: 3s^{2} 3p^{3}$
$D: 3s^{2} 3p^{4}$
The correct order of first ionization enthalpy for them is:

The first ionization enthalpies of $C$,$N$,and $F$ are $1086$,$1402$,and $1681 \, kJ \, mol^{-1}$ respectively. Which of the following values is the most likely first ionization enthalpy of $O$ ($1310$ or $1510 \, kJ \, mol^{-1}$)?

Which of the following has the highest first ionisation energy?

The element having the highest first ionization enthalpy is