An amorphous solid $$(X)$$  burns in air to form a gas $$(Y)$$  which turns lime water milky. This gas decolourises aqueous solution of acidified $$KMn{O_4}.$$  Gas $$(Y)$$ reacts with oxygen to give another gas $$(Z)$$ which is responsible for acid rain. $$X, Y$$  and $$Z$$ are

	$$X$$	$$Y$$	$$Z$$
(a)	$$C$$	$$CO$$	$$C{O_2}$$
(b)	$$S$$	$$S{O_2}$$	$$S{O_3}$$
(c)	$$P$$	$${P_2}{O_3}$$	$${P_2}{O_5}$$
(d)	$$S$$	$$S{O_3}$$	$${H_2}S{O_4}$$

Solution :
$$\mathop S\limits_{\left( X \right)} + {O_2} \to \mathop {S{O_2}}\limits_{\left( Y \right)} $$
$$\mathop {S{O_2}}\limits_{\left( Y \right)} + Ca{\left( {OH} \right)_2} \to $$     $$\mathop {CaS{O_3} \downarrow }\limits_{{\text{white ppt}}{\text{.}}} + {H_2}O$$
$$\mathop {2KMn{O_4}}\limits_{{\text{Purple}}} + \mathop {5S{O_2}}\limits_{\left( Y \right)} + 2{H_2}O \to $$      $${K_2}S{O_4} + \mathop {2MnS{O_4}}\limits_{{\text{Colourless}}} + 2{H_2}S{O_4}$$
$$\mathop {2S{O_2}}\limits_{\left( Y \right)} + {O_2} \to \mathop {2S{O_3}}\limits_{\left( Z \right)} $$
$$\mathop {S{O_3}}\limits_{\left( Z \right)} + {H_2}O \to {H_2}S{O_4}$$     $$\left( {{\text{responsible for acid rain}}} \right)$$