Identify the anion present in the following compounds :
(i) Compound X on heating, with copper turnings and concents sulphuric acid liberates a reddish brown gas.
(ii) When a solution of compound Y is treated with silver nitrate solution a white precipitate is obtained which is soluble in excess of ammonium hydroxide solution.
(iii) Compound Z which on reacting with dilute sulphuric acid liberates a gas which lime lune water milky, but the gas has no effect on acidified potassium dichromate solution.
(iv) Compound L on reacting with barium chloride solution gives a white precipitate insoluble in dilute hydrochloric acid or dilute nitric acid.