Which of the following has the least ionization potential?

The first ionisation potential $(IP)$ of the elements $Na$,$Mg$,$Si$,$P$,$Cl$ and $Ar$ are $5.14$,$7.65$,$8.15$,$10.49$,$12.97$ and $15.76 \ eV$,respectively. The $IP$ (in $eV$) of $K$ is closest to

What is the order of first,second,and third ionisation enthalpy? Why?

The correct order of ionisation energy for comparing carbon,nitrogen,and oxygen atoms is:

Generally,the first ionisation energy increases along a period. But there are some exceptions. The one which is not an exception is

The first ionisation enthalpies for three elements are $1314$,$1680$ and $2080 \, kJ \, mol^{-1}$,respectively. The correct sequence of the elements is