The energy profiles for the two possible mechanisms of the following reaction,


are given below

Consider the following substrates (I to IV) for the above reaction
$\begin{aligned} & \text { I: } \mathrm{R}_1=\mathrm{R}_2=\mathrm{R}_3=\mathrm{H} \\ & \text { II: } \mathrm{R}_1=\mathrm{C}_2 \mathrm{H}_5 ; \mathrm{R}_2=\mathrm{R}_3=\mathrm{H} \\ & \text { III: } \mathrm{R}_1=\mathrm{C}_2 \mathrm{H}_5 ; \mathrm{R}_2=\mathrm{CH}_3 ; \mathrm{R}_3=\mathrm{H} \\ & \text { IV: } \mathrm{R}_1=\mathrm{C}_2 \mathrm{H}_5 ; \mathrm{R}_2=\mathrm{R}_3=\mathrm{CH}_3\end{aligned}$
Choose the correct statement(s).

• Correct answer
  A

  The reaction mechanism changes from the one shown in Figure Y to that in Figure X , as one changes the substrate from I to IV.
• Correct answer
  B

  Considering the mechanism corresponding to Figure X for substrates I to IV, the correct order of $\Delta E$ is: $\Delta E_{\mathrm{I}} \lt \Delta E_{\mathrm{II}} \lt \Delta E_{\mathrm{III}} \lt \Delta E_{\mathrm{IV}}$
• Correct answer
  C

  The reaction for substrate I follows $2^{\text {nd }}$ order kinetics and that for IV follows $1^{\text {st }}$ order kinetics.
• Correct answer
  D

  If $\mathrm{CN}^{-}$is taken in large excess, it is difficult to ascertain if the reaction follows mechanism corresponding to energy profile in Figure X or that in Figure Y .

Hence, the correct answer is options: 'A', 'B', 'C', 'D'.