The correct order of the second ionisation potential of carbon, nitrogen, oxygen and fluorine is

Options

A. `F gt Ogt N gt C`
B. `O gt F gt N gt C`
C. `O gt N gt F gt C`
D. `C gt N gt O gt F`

Answer

B

Explanation

The second ionization potential corresponds to the removel of electron from an isolated unipositive ion. The electron configurations of unipositive ions of `C,N, O`, and `F` are as follows:
`C^(+)(Z = 6) rArr 1s^(2)2p^(2)2p^(1)`
`N^(+)(Z = 7) rArr 1s^(2)2p^(2)2p^(2)`
`O^(+) (Z = 8) rArr 1s^(2) 2p^(2)2p^(3)`
`F^(+) (Z = 9) rArr 1s^(2) 2p^(2)2p^(4)`
Number of shells in these ubnipositive ions is the same, thus, the ionization potential is expected to increase with the increase of nuclear charge. However, `O^(+)` has exactly filled `p` subshell, thus, the removel of an electron from `O^(+)` is relatively difficult. Thus, the correct order is
`O gt F gt N gt C`