Treatment of a gas 'X' with a freshly prepared ferrous sulphate solution gives a compound 'Y' as a brown ring. The compounds X and Y are.

A

NO and [Fe(NO)]SO$$_4$$

B

NO$$_2$$ and [Fe(NO$$_2$$)]SO$$_4$$

C

N$$_2$$O and [Fe(N$$_2$$O)]SO$$_4$$

D

N$$_2$$O$$_4$$ and [Fe(N$$_2$$O$$_4$$)]SO$$_4$$