# Arrange the following in order of increasing ionization energies: Ar, Se, S.

$\begin{array}{1 1} Ar,Se,S \\ Se,S,Ar \\ S,Se,AR \\ Se,Ar ,S\end{array}$

Ionization energy increases from left to right in a period and decreases from top to bottom in a group.
If we compare Se and S, Se is below S in group VIA therefore ionization energy of Se must be lower than that of S.
If we compare S and Ar which are in the same period, the ionization energy of S is less than that of Ar.
Therefore, the correct order (of increasing ionization energy) is Se, S, Ar.