(a) Non-metal “A” is nitrogen because it is the largest constituent of air which constitute around 78% of the gases. B is Ammonia, C is Nitrogen-di-oxide and D is Nitric acid.
When heated with H2 in 1:3 ratio in the presence of a catalyst (Fe) following reaction takes place.
3N2 + 3H2 → 2NH3
On heating Nitrogen with O2, it gives nitrogen-di-oxide
N2 + 3O → 2NO2
When nitrogen dioxide is passed into the water in the presence of air, it gives Nitric acid
NO2 +H2O → HNO3
(b) Nitrogen belongs to group 15.