Consider the reaction, $\text{2A\hspace{0.17em}+\hspace{0.17em}B\hspace{0.17em}}\to$products. When concentration of B alone was doubled, the  half– life did not change. When the concentration of A alone was doubled. The rate increased by two times. The unit of rate constant for this reaction is

Since doubling the concentration of B does not change half life, the reaction is of 1^st or5der w.r.t. B. order of reaction with respect to A = 1 because rate of reaction doubles when concentration of A is doubled keeping concentration of B constant.

 $\therefore$Order of reaction = 1 + 1 = 2 and units of second order reaction are $Lmo{l}^{-1}{\sec }^{-1}$.