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. 0n heating with `O_(2)` it gives an oxide C. If this oxide is passed into water in the presence of air, it gives an acid D which acts as a strong oxidising agent. 
(a) Identify A, B, C and D.
(b) To which group of the periodic table does this non-metal belongs? 

Explanation

(a) The available information suggests that the non-metal A is nitrogen (N) and its molecular form is `N_(2)`. It is the major constituents of air (about 79 per cent by volume). It reacts with `H_(2)` upon heating m the presence of iron catalyst (Fe) to form ammonia `(NH_(3))` gas(B)
`underset(("A"))(N_(2)(g))+3H_(2)(g) underset("heat")overset("Fe")rarr underset(("B"))(2NH_(3)(g))`
Upon heating with oxygen, nitrogen forms intially nitric oxide (NO) and then nitrogen dioxide (C ). The latter reacts with water in the presence of oxygen to form nitric acid (D). The acid acts as strong oxidising agent.
`N_(2)(g) + O_(2)(g) overset("heat")rarr 2NO(g)`
`2NO(g) + O_(2)(g) overset("heat")rarr underset(("C"))(2NO_(2))(aq)`
`4NO_(2)(g) + 2H_(2)O(aq) + O_(2) (g) rarrunderset(("D"))(4HNO_(3))(aq)`
(b) The element nitrogen is the first member of group 15 of the Long form of Perodic Table.