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Q.
The correct order of $2^{nd}$ ionisation potential of carbon, nitrogen, oxygen and fluorine is
NTA AbhyasNTA Abhyas 2022
Solution:
$C\left(6\right)1s^{2}2s^{2}2p_{x}^{1}2p_{y}^{1}$
$N\left(7\right)1s^{2}2s^{2}2p_{x}^{1}2p_{y}^{1}2p_{z}^{1}$
$O\left(8\right)1s^{2}2s^{2}2p_{x}^{2}2p_{y}^{1}2p_{z}^{1}$
$F\left(9\right)1s^{2}2s^{2}2p_{x}^{2}2p_{y}^{2}2p_{z}^{1}$
$O$ has highest $2^{nd}$ ionisation potential i.e ionisation energy because after losing one electron, it acquires noble gas configuration.
$F$ is smaller than $N$ , therefore, it has higher second ionisation potential. $C$ has least due to bigger size.