A non-metal A which is the largest constituent of air, when heated with H2 in 1 : 3 ratio in the presence of catalyst (Fe) gives a gas B. On heating with O2, it gives an oxide C. If this oxide is passed into water in the presence of air, it gives and acid D which act as a strong oxidising agent.   (2 marks)

(a) Identify A, B, C and D.

(b) To which group of periodic table does this non-metal belong?