Sulphur dioxide is passed through an acidified aqueous solution of ferric sulphate. The change observed and the reason are

1. Ayellow-brown solution turns pale green as $\mathrm{Fe}{}^{3+}$ is reduced to $\mathrm{Fe}{}^{2+}$ by $\mathrm{SO}{}_2$
2. Bsolution turns green as $\mathrm{Fe}{}^{3+}$ is oxidised to $\mathrm{FeO}{}_4{}^{2-}$
3. Cno change as $\mathrm{SO}{}_2$ is only an acidic oxide
4. Da white precipitate of $\mathrm{FeSO}{}_3$ forms