For a reaction A → B, it is found that the rate of the reaction quadruples when the concentration of A is doubled. The rate for the reaction is Rate = k [A]x, where the value of x is:
2
Rate = k[A]x
When the rate of the reaction quadruples,
Rate1 = 4 Rate
k[2A]x = 4 k[A]x
[2A]x/[A]x = 4
so, x=2