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:
\( \mathrm{NO} \) and \( [\mathrm{Fe(NO)}]\mathrm{SO_4} \)
\( \mathrm{NO_2} \) and \( [\mathrm{Fe(NO_2)}]\mathrm{SO_4} \)
\( \mathrm{N_2O} \) and \( [\mathrm{Fe(N_2O)}]\mathrm{SO_4} \)
\( \mathrm{N_2O_4} \) and \( [\mathrm{Fe(N_2O_4)}]\mathrm{SO_4} \)