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

Non-metal A is nitrogen gas `N_(2)` since. the percentage of `N_(2)` in air is largest. i.e., 78%.
When `N_(2)` is heated with `H_(2)` in 1:3 ratio in presence of Fe as catalyst, (a) it forms ammonia `(NH_(3))`.
`underset("Nitrogen")(N_(2)(g))+underset("Hydrogen")(3H_(2)(g))overset(Fe)hArrunderset("Ammonia")(2NH_(3)(g))`
Thus, B is ammonia`(NH_(3))` gas. Gas B, when heated with `O_(2)`, it forms nitric oxide (NO). NO further gets oxidised to `NO_(2)" by "O_(2)` of the air. Thus, C is `NO_(2)` (nitrogen dioxide).
`4NH_(3)(g)+5O_(2)(g)oversetDeltato4NO(g)+6H_(2)O(g)`
`2NO(g)+O_(2)(g)to2NO_(2)(g)`
When this oxide is passed into water in the presence of air `(O_(2))`, it gives nitric acid `(HNO_(3))` which acts as a strong oxidising agent.
Thus, D is nitric acid `( HNO_(3))`
`4NO_(2)+2H_(2)O+O_(2)to4HNO_(3)`
(b) The nonmetal belongs to group 15 or VA because N has 5 valence electrons (electronic configuration is 2, 5).