For zero order reaction, ${\mathrm{t}}_{1/2}$ will be (${\mathrm{A}}_0$ is the initial concentration, $\mathrm{K}$ is rate constant)

The depletion of ozone involves the following steps:
Step 1: ${\mathrm{O}}_3\underset{{\mathrm{K}}_1}{\overset{{\mathrm{K}}_1}{\rightleftharpoons }}{\mathrm{O}}_2+\mathrm{O}$ (fast)

Step 2: ${\mathrm{O}}_3+\mathrm{O}\underset{\mathrm{K}}{\to }2{\mathrm{O}}_2$ (slow)

The predicted order of the reaction will be

$\mathrm{A}+\mathrm{B}⟶\mathrm{C}; \mathrm{\Delta H}=+60 \mathrm{kJ}/\mathrm{mol}$

${\mathrm{E}}_{{\mathrm{a}}_{\mathrm{f}}}$ is $150 \mathrm{kJ}$. What is the activation energy for the backward reaction?