Which of the following elements are at the peaks of the ionization energy trend?

The third ionisation enthalpy is highest in

Electronic configurations of four elements $A$,$B$,$C$,$D$ are given below:
$A$) $1s^2 2s^2 2p^6 3s^1$
$B$) $1s^2 2s^2 2p^6 3s^2 3p^1$
$C$) $1s^2 2s^2 2p^6 3s^2$
$D$) $1s^2 2s^2 2p^6 3s^2 3p^2$
The correct order of first ionization enthalpy of these elements is:

In the photoelectric effect,if the work functions of $Li$,$Na$,and $Rb$ are $2.41 \ eV$,$2.30 \ eV$,and $2.09 \ eV$ respectively,the work function of $K$ could approximately be in $eV$?

Which of the following presents the correct order of second ionization enthalpies of $C$,$N$,$O$ and $F$?

Element having highest $I.P.$ value is