Which of the following has lowest ionisation energy

Options

A. Oxygen
B. Nitrogen
C. Fluorine
D. Sulphur

Answer

D

Explanation

Among oxygen, nitrogen, fluorine and sulphur, the lowest ionisation energy is of sulphur.
As their first ionisation values indicated below.
`N = 1402.1 kJ//mol, O = 1313.7 kJ//mol`,
`F = 1680.8 kJ //mol, S = 999.4 kJ //mol`.
As down the group, the number of inner shells increases. Therefore ionisation energy decreases due to screening effect.