Question

Which has maximum ionisation potential?

• A. $N$
• B. $O$
• C. $O^{+}$
• D. $Na$

Answer 1

Answer: (C)

$O^{+}$

$N\left(7\right)$ and $O^{+}(8-1=7)=1s^{2}2s^2\underset{\text{Maximum multiplicity most stable}}{\underset{}{2p_x^{1}2p_y^{1}2p_z^1}}$
$P=1s^2,2s^{2}2p_x^2,2p_y^1,2p_z^1$
Ionisation potential is dependent on the value of $Z$.
$Z$ of $O^{+}\left(8\right)>Z$ of $N\left(7\right)$
Thus, ionisation potential of $O^{+}>N$
$Na$ with one valence electron has least ionisation potential.