Catalysts in the following reactions are

(I) $\mathrm{CH}_3 \mathrm{COOCH}_3(l)+\mathrm{H}_2 \mathrm{O}(l)\longrightarrow \mathrm{CH}_3 \mathrm{COOH}(a q)+\mathrm{CH}_3 \mathrm{OH}(l)$

(II) $2 \mathrm{SO}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{SO}_3(\mathrm{~g})$

(III) $2 \mathrm{SO}_2(\mathrm{~g})+\mathrm{O}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{SO}_3(\mathrm{~g})$

(IV) $\mathrm{N}_2(\mathrm{~g})+3 \mathrm{H}_2(\mathrm{~g}) \longrightarrow 2 \mathrm{NH}_3(\mathrm{~g})$

For $\mathrm{As}_2 \mathrm{~S}_3$ sol, the most effective coagulating agent is

Which of the following is true for spontaneous adsorption?

The charge of " $\mathrm{SnO}_2-\mathrm{sol}^{\prime}$ in alkaline and acidic medium are respectively

(Hint $\mathrm{SnO}_2$ is amphoteric oxide)