$(a) 2SO_2(g) +O_2(g) \quad \underrightarrow {NO(g)} \quad 2SO_3(g)$
(b) Hydrolysis of aqueous sucrose solution in the presence of aqueous mineral acid
$(c) 2H_2O_2(l) \quad \underrightarrow {Pt(s)} \quad 2H_2O(l)+O_2(g)$
(d) Hydrolysis of liquid in the presence of aqueous mineral acid
