(a) Identify the anions in the following. 
(i) Salt A gives off a gas with suffocating odour of burning sulphur with dilute hydrochloric acid.
(ii) Salt B gives reddish brown gas on heating with concentrated sulphuric acid.
(iii) Salt C gives off a gas with smell of rotten eggs with dilute nitric acid.
(iv) An aqueous solution of salt D gives a white precipitate with Barium chloride solution which is
insoluble in dilute hydrochloric acid.