A teacher gave a student two salts (A) and (B) told him to identify these salts. The student heated salt (A) strongly and observed two oxides of sulphur. He added NaOH solution to the aqueous solution of (A) and observed a green precipitate, which turned brown on exposure to air.When he took salt (B) to flame test, green colour was observed. On heating salt (B) with a solid compound (X) and concentrated sulphuric acid, orange red vapours are evolved. When this gas is passed through an aqueous solution of a base, the solution turns yellow.- The salt (A) can be:
(1) Fe2(SO4)3
(2) FeSO4
(3) FeSO4 · 7H2O
(4) both (b) and (c)