A reaction A_2+ B_2 → 2 AB occurs by the following mechanism: A_2 → A + A (slow); A + B_2 → AB + B (fast); A + B → AB (fast) Its order would be:

A reaction $\displaystyle \mathrm{A}_{2}+\mathrm{B}_{2} \longrightarrow 2 \mathrm{AB}$ occurs by the following mechanism : \[\begin{aligned} & \mathrm{A}_{2} \rightarrow \mathrm{~A}+\mathrm{A} \text { (slow) } \\ & \mathrm{A}+\mathrm{B}_{2} \rightarrow \mathrm{AB}+\mathrm{B} \text { (fast) } \\ & \mathrm{A}+\mathrm{B} \rightarrow \mathrm{AB} \text { (fast) } \end{aligned} \] Its order would be :