Amongst the various ores of a metal (M) (sulphide, carbonates, oxides, hydrated or hydroxides), two ores [X] and [Y] show the following reactivity:
(i) [X] on calcination gives a black solid (S), carbon dioxide and water.
(ii) [X] dissolved is dilute HCl, on reaction with KI gives a white precipitate (P) and iodine.
(iii) [Y] on roasting gives metal (M) and a gas $$(G_1)$$ which turns acidified $$K_2Cr_2O_7$$ solution green.
(iv) [Y] on reaction with dil. HCl gives a white precipitate (Q) and another gas $$(G_2)$$ which turns lead acetate solution black, and also reacts with gas $$(G_1)$$ to precipitate colloidal sulphur in presence of moisture.