$[X] + H_2SO_4 \longrightarrow [Y]$ colourless with irritating smell. $[Y] + K_2Cr_2O_7 + H_2SO_4 \longrightarrow$ Green solution. [X] and [Y] are

Question

(a) $SO_3^{2-}, SO_2$
(b) $Cl^-, HCl$
(c) $S^{2-}, H_2S$
(d) $CO_3^{2-}, CO_2$