2A+B→ Product When conc. of B is doubled, the half life did not change, hence reaction is of first order w.r.t. B. When concentration of A is doubled, reaction rate is doubled, hence reaction is of first order w.r.t. A. Hence over all order of reaction is 1+1=2 So, unit of rate constant mol−1 lit s−1. Hence, (A) is correct.