Question

Give reasons for the following.
$a.$ Oxygen is a gas but sulphur is a solid.
$b.$ ${BiH}_3$ is the strongest reducing amongst all hydrides of Group $15$ elements.

Answer 1

Oxygen exists as a gas due to a smaller size. The intermolecular forces between oxygen are weak van der Waals forces. So, oxygen exists as a gas. Sulphur exists as a solid because the atoms are held by strong covalent bonds. Which binds the atoms closely and strongly. Hence Sulphur exists as a solid.

Among the reducing strength of Group-I5 elements, ${BiH}_3$ (Bismuthine) is a strong reducing agent. ${BiH}_3$ have a great size central atom and its tending to form a covalent bond with hydrogen decreases. Due to less bond strength, ${BiH}_3$ is unstable with the decrease in stability reducing character increases. Hence, ${BiH}_3$ is the strongest reducing agent in group 15.