Which of the following is an example of pseudo unimolecular reaction? 

When in any chemical reaction, one of the reactant is present in large excess, then the second-order reaction becomes first-order reaction and is known as pseudo unimolecular reaction e.g., 

${\mathrm{CH}}_3{\mathrm{COOCH}}_3+{\mathrm{H}}_2\mathrm{O}\stackrel{{\mathrm{H}}^{+}}{\to }{\mathrm{CH}}_3\mathrm{COOH}+{\mathrm{CH}}_3\mathrm{OH}$

in this reaction molecularity is 2 but order of reaction is found to be first order experimentally, so it is an example of pseudo unimoelcular reaction.