Give reasons for the following :
(i) Oxygen is a gas but sulphur is a solid.
(ii) acts as a powerful oxidising agent.
(iii) is the strongest reducing agent amongst all the hydrides of Group 15 elements.
(i) Due to small size and high electronegativity, oxygen forms multiple bonds and thus forms diatomic. molecule are held together by weak van der Waals forces of attraction which can be easily overcome by collisions at room temperature. Therefore is gas at room temperature. On the other hand due to higher tendency for catenation and lower tendency for multiple bonds, intra-atomic has strong forces of attraction which cannot be overcome by collisions. Therefore S is solid at room temperature.
(iii) is a powerful oxidising agent due to its high energy content than oxygen and hence decomposes to give diatomic oxygen and atomic oxygen
(iii) As we move down the group, the E-H bond length increases and their strength decreases. Bi-H bond is the weakest. It can break easily and evolves gas which acts as the reducing agent.