For the reaction, A+B⟶ Products On doubling the initial concentration of A only, the rate of reaction is also doubled, therefore Rate ∝[A]1 Let initially rate law is Rate =k[A][B]y If concentration of and both are doubled, the rate gets changed by a factor of 8 . 8× Rate =k[2 A][2 B]y…( iii) [∵ Rate ∝[A]1] Dividing Eq. (iii) by Eq. (ii), 8=2×2y4=2y∴y=2 Hence, rate law is, rate =k[A][B]2