Compound ′A′ (molecular formula C3H8O) is treated with acidified potassium dichromate to form a product ′B′ (molecular formula C3H6O). ′B′ forms a shining silver mirror on warming with ammoniacal silver nitrate. ′B′ when treated with an aqueous solution of NH2CONHNH2, HCl and sodium acetate gives a product ′C′. Identify the structure of ′C′.