b
Elements in the 2nd period are: Period Elements II nd
Li Be BC N O F Nel In a period from left to right, ionization potential increases. But in case of nitrogen
and oxygen, nitrogen has more ionization potential than oxygen atom due to stable electronic configuration of nitrogen. $7 N=1 s^{2}, 2 s^{2} 2 p^{3} \mid$
$\uparrow\|\| \|$
(Stable configuration) $80=1 s^{2}, 2 s^{2} 2 p^{4}$ (Unstable configuration) Nitrogen has stable configuration as
the p-orbitals are half-filled completely. So, more energy is required to remove an electron from the outermost orbit of nitrogen atom. So, $\mathrm{N}_{2}$, has 14.5 value of ionisation potential.