sp³d² hybridization is not displayed by :

In which of the following reactions, hydrogen peroxide acts as an oxidizing agent ?

Identify the pollutant gases largely responsible for the discoloured and lustreless nature of marble of the Taj Mahal.

A metal ‘M’ reacts with nitrogen gas to afford ‘M₃N’. ‘M₃N’ on heating at high temperature gives back ‘M’ and on reaction with water produces a gas ‘B’. Gas ‘B’ reacts with aqueous solution of CuSO₄ to form a deep blue compound. ‘M’ and ‘B’ respectively are :