\([\mathrm{X}]+\) dil. \(\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow[\mathrm{Y}]:\) Colourless, suffocating gas
\([\mathrm{Y}]+\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}+\mathrm{H}_{2} \mathrm{SO}_{4} \rightarrow\) Green colouration of solution
Then, \([\mathrm{X}]\) and \([\mathrm{Y}]\) are
(A) \(\mathrm{SO}_{3}^{2-}, \mathrm{SO}_{2}\)
(B) \(\mathrm{Cl}^{-}, \mathrm{HCl}\)
(C) \(\mathrm{S}^{2-}, \mathrm{H}_{2} \mathrm{~S}\)
(D) \(\mathrm{CO}_{3}^{2-}, \mathrm{CO}_{2}\)