For a reaction of the type A + B → products, it is observed that doubling the concentration of A causes the reaction rate to be four times as great, but doubling the amount of B does not effect the rate. The rate equation is -

(1) Rate = K [A][B]
(2) Rate = K [A]²
(3) Rate = K[A]²[B]
(4) Rate = K[A]²[B]²