Arrange the elements N, P, O and S in the order of
i) increasing first ionisation enthalpy.
ii) increasing non-metallic character.
Give reason for the arrangement assigned.

Answer

A

Explanation

The placing of elements are as

i) Ionisation enthalpy of nitrogen `(._(7)N=1s^(2), 2s^(2), 2p^(3))` is greater than oxygen `(._(8)O)=1s^(2), 2s^(2), 2p^(4))` due to extra stable exactly half-filled 2p-orbitals. Similarly, ionisation enthalpy of phosphorours. `(._(15)P=1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(3))` is greater than sulphur `(._(16)S=1s^(2), 2s^(2), 2p^(6), 3s^(2), 3p^(4))`
On moving down the group, ionisation enthalpy decreases with increasing atomic size. So, the order is
`SltPltOltN to` First ionisation enthalpy increases.
ii) Non-metallic character across a period (left to right) increases but on moving down the group it decreases. So, the order is
`P lt S lt N lt O to` Non metallic character increases.