The rate constant is same for $3$ reactions of order $\mathrm{I}$, $\mathrm{II}$ and $\mathrm{III}$, respectively, the unit of concentration being in moles per litre. If the concentration of the reactant is unity, the rates of reaction ${\mathrm{R}}_1, {\mathrm{R}}_2, {\mathrm{R}}_3$ will be

• Correct answer
  A

  ${\mathrm{R}}_1={\mathrm{R}}_2={\mathrm{R}}_3$
• B

  ${\mathrm{R}}_1<{\mathrm{R}}_2<{\mathrm{R}}_3$
• C

  ${\mathrm{R}}_1>{\mathrm{R}}_2>{\mathrm{R}}_3$
• D

  ${\mathrm{R}}_1={\mathrm{R}}_2\ne {\mathrm{R}}_3$

Hence, the correct answer is option: 'A'.