Ionization energy is highest for

Which of the following represents the correct order of increasing first ionization enthalpy for $Ca, Ba, S, Se$ and $Ar$?

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 orders for ionisation energy is correct?

Which of the following configurations represents atoms of the elements having the highest second ionization energy?

The second ionization energy is maximum for