A hypothetical reaction `A_(2) + B_(2) rarr 2AB` follows the mechanism as given below:
`A_(2) hArr A+A ("fast")`
`A+B_(2) rarr AB+B` (slow)
`A+B rarr AB` (fast)
The order of the overall reaction is

Options

A. 0
B. 1
C. 2
D. `3 // 2`

Answer

D

Explanation

`A_(2)+B_(2) to 2AB`, `A_(2) to A+A` (Fast),
`A+B_(2) to AB+B` (Slow)
Rate law `=k[A][B_(2)]` put value of [A] from Ist reaction since A is intermediate `sqrt(k[A_(2)])=A`
`:. "Rate law equation"=Ksqrt(k[A_(2)][B_(2)])`
`:. "Order"=(1)/(2)+1=(3)/(2)`