Which of the following has the least ionization potential?

Which of the following has the least ionization potential?

The correct increasing order of ionisation enthalpy of $He, Li^{+}, Be^{2+}$ is

Outermost electronic configurations of four elements $A, B, C, D$ are given below:
$A: 3s^{2}$
$B: 3s^{2} 3p^{1}$
$C: 3s^{2} 3p^{3}$
$D: 3s^{2} 3p^{4}$
The correct order of first ionization enthalpy for them is:

The second ionisation potential of an element $M$ is the energy required to

The first ionisation energies (in $kJ \ mol^{-1}$) of four consecutive elements of the second period are given in the options. The first ionisation energy of nitrogen is