Name the anion present in the following compounds:
a)When barium chloride solution is added to a solution of compound b a white precipitate in sellable in dilute hydrochloric acid is formed.
b) The action of heat on the insoluble compound C produces a gas which turns limewater turbid.
c) Compound D when warmed with dilute sulphuric acid gives a gas which turns acidified dichromate solution green.