Select the correct statement about elements of group 15.

The inert pair effect is the redundancy of s-electrons to participate in bonding. This effect is more pronounced on heavier elements. This depicts that the inert pair effect is increased by moving down the group.

Nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi) are the elements in group-15. For group-15 elements, the stability of the +5 oxidation state diminishes along the group, while the stability of the +3 oxidation state increases.

The atomic sizes of As, Sb, and Bi are in the order Bi>Sb>As. Arsenic and antimony are lighter elements than Bismuth.

Therefore,

• Bi³⁺>Sb³⁺ is the stability of the +3 oxidation state of Bi and Sb.
• As⁵⁺>Sb⁵⁺>Bi⁵⁺ is the stability of the +5 oxidation state of As, Sb, and Bi.

Disproportionate reaction of nitrogen oxide is:

$3\mathrm{H}\stackrel{+3}{\mathrm{N}}{\mathrm{O}}_2\to \mathrm{H}\stackrel{+5}{\mathrm{N}}{\mathrm{O}}_3+{\mathrm{H}}_2\mathrm{O}+2\stackrel{+2}{\mathrm{N}}\mathrm{O}$

There is slight increase in atomic size from As to Bi because of having filled d or f orbitals.