Question

What is the order of reaction if the plot of rate vs [A]² is a straight line?

Answer 1

If a plot of rate vs [A]² gives a straight line, then the reaction is second order with respect to reactant A.

The general rate law is 

Rate = k[A]ⁿ

If plotting rate vs. [A]² gives a straight line, this implies

Rate ∝ [A]²

Therefore, the order of reaction with respect to A is

n = 2

And hence, the overall order of the reaction is 2, assuming A is the only reactant.