All of the following are the true statements concerning reaction orders except :

A The rate of a zero-order reaction is constant

B After three half-lives, a radioactive sample will have one-ninth of its original concentration.

C The unit for the rate constant for first order reaction are s^-1.

D If doubling the concentration of a reaction doubles the rate of the reaction, then the reaction is first order in that reactant.

Correct Answer: Option B