Among the following unimolecular reaction is

$\mathrm{a}) {\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+{\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$

Total number of reactant molecules taking part in elementary reaction is 2. So, it is a bimolecular reaction.

$\mathrm{b}) 2\mathrm{NO}+{\mathrm{O}}_2\to 2{\mathrm{NO}}_2$

Total number of reactant molecules taking part in elementary reaction is 3. Hence, it is a termolecular reaction.

$\mathrm{c}) \mathrm{Decomposition} \mathrm{of} {\mathrm{H}}_2{\mathrm{O}}_2$

The overall reaction is $2{\mathrm{H}}_2{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}+{\mathrm{O}}_2$

The proposed mechanism is given below.

${\mathrm{H}}_2{\mathrm{O}}_2\to {\mathrm{H}}_2\mathrm{O}+\left(\mathrm{O}\right); \mathrm{slow} \mathrm{step}$

${\mathrm{H}}_2{\mathrm{O}}_2+\left(\mathrm{O}\right)\to {\mathrm{H}}_2\mathrm{O})+{\mathrm{O}}_2; \mathrm{fast} \mathrm{step}$

$\mathrm{Rate} =\mathrm{k}\left[{\mathrm{H}}_2{\mathrm{O}}_2\right] \left(\mathrm{from} \mathrm{slow} \mathrm{step}\right)$

Therefore, the reaction is unimolecular.

$\mathrm{d}) \mathrm{Reaction} \mathrm{between} {\mathrm{NO}}_2 \mathrm{and} {\mathrm{F}}_2$

The overall reaction is $2{\mathrm{NO}}_2+{\mathrm{F}}_2\to 2{\mathrm{NO}}_2\mathrm{F}$

The proposed mechanism is

${\mathrm{NO}}_2+{\mathrm{F}}_2\to {\mathrm{NO}}_2\mathrm{F}+\left(\mathrm{F}\right); \mathrm{slow} \mathrm{step}$

${\mathrm{NO}}_2+\left[\mathrm{F}\right]\to {\mathrm{NO}}_2\mathrm{F}; \mathrm{fast} \mathrm{step}$

$\mathrm{Rate} =\mathrm{K}\left[{\mathrm{NO}}_2\right]\left[{\mathrm{F}}_2\right] ( \mathrm{from} \mathrm{slow} \mathrm{step})$

$\therefore \mathrm{The} \mathrm{reaction} \mathrm{is} \mathrm{bimolecular}.$