An aqueous solution of a gas (X) gives the following reactions :
(i) It turns an acidified K2Cr2O7 solution green.
(ii) On boiling it with H2O2, cooling it and then adding an aqueous solution of BaCl2, a precipitate insoluble in dilute hydrochloric acid is obtained.
(iii) On passing H2S in the solution a white turbidity is obtained.
Identify (X).