A sodium salt X gives a colourless pungent gas with dilute $H X_{2} SO X_{4}$ . The gas turns lime water milky, the milkiness disappears on passing excess gas, and the gas decolourises acidified $KMnO X_{4}$ . X and the species responsible for the clearing are

Answer: B

Decolourising acidified

KMnO X_{4}

and the pungent smell rule out

CO X_{2}

and point to

SO X_{2}

SO X_{2} + Ca (OH) X_{2} CaSO X_{3} + H X_{2} O

gives the milkiness and

CaSO X_{3} + SO X_{2} + H X_{2} O Ca (HSO X_{3}) X_{2}

(soluble) clears it. The salt is sodium sulphite;

CO X_{2}

would not decolourise permanganate and

H X_{2} S

is not given by sulphite.