Which among the following elements has the highest first ionization enthalpy?

In a group of elements,as the atomic number increases,which of the following is $NOT$ observed?

The electronic configurations of elements $A, B$ and $C$ are $[He] 2s^1$,$[Ne] 3s^1$ and $[Ar] 4s^1$ respectively. Which one of the following orders is correct for the first ionization potentials (in $kJ \ mol^{-1}$) of $A, B$ and $C$?

Which of the following has the highest first ionisation energy?

The order of the magnitude of first ionisation potentials of $Be$,$B$,$N$ and $O$ is

The first four ionization energy values of an element are $191$,$578$,$872$ and $5962 \ kcal$. The number of valence electrons in the element is