The rate constant is same for 3 reactions of order I , II and III , respectively, the unit of concentration…

Suppose ${\mathrm{R}}_1, {\mathrm{R}}_2$ and ${\mathrm{R}}_3$ are the rates of three reactions of first, second and third-order, respectively, and $\mathrm{k}$ is the rate constant for all three reactions.

$\left[\mathrm{A}\right]$ being the concentration of reaction $\mathrm{A}$ in mole per litre.

Now,