Question

The correct order of $2^{nd}$ ionisation potential of carbon, nitrogen, oxygen and fluorine is

• A. $C>N>O>F$
• B. $O>N>F>C$
• C. $O>F>N>C$
• D. $F>O>N>C$

Answer 1

Answer: (C)

$C\left(6\right)1s^{2}2s^{2}2p_x^{1}2p_y^1$
$N\left(7\right)1s^{2}2s^{2}2p_x^{1}2p_y^{1}2p_z^1$
$O\left(8\right)1s^{2}2s^{2}2p_x^{2}2p_y^{1}2p_z^1$
$F\left(9\right)1s^{2}2s^{2}2p_x^{2}2p_y^{2}2p_z^1$
$O$ 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.