NEET Class neet Answered

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

O>F>N>C. 

Nitrogen: [He] 2s² 2p³  

Oxygen: [He] 2s² 2p⁴   

Florine: [He] 2s² 2p⁵  

Carbon: [He] 2s² 2p² 

After removing one electron: 

Nitrogen: [He] 2s² 2p²  - After removal of one more electron, it will have only one electron in its outermost p-subshell.

Oxygen: [He] 2s² 2p³  -  After removal of one more electron, it will have two electrons in p-subshell which makes it very unstable.

                                     Also it is difficult to remove electron form stable configuration (half filled). More energy is required to remove electron, so the ionisation potential is very high.

Fluorine: [He] 2s² 2p⁴  - After removal of one more electron, it will occupy stable half-filled configuration. 

Carbon: [He] 2s² 2p¹ -  After removal of one more electron, it will occupy ideal gas configuration. Hence it will easily give away second electron having very low second IP.