The order of kinetics of $S_{N}1$ reactions is:

First

The correct answer is Option (1) → First

SN1 reactions follow first order kinetics because the rate depends only on the concentration of the substrate.

Explanation

Option 1: First

In SN1 reactions, the rate determining step is the formation of carbocation. This step involves only the substrate and not the nucleophile. Hence, rate depends on substrate concentration only.

Rate = k[RX]

Option 2: Zero

Zero order reactions are independent of concentration, which is not true for SN1 reactions.

Option 3: Second

Second order kinetics is followed by SN2 reactions where both substrate and nucleophile affect the rate.

Option 4: Third

SN1 reactions never follow third order kinetics since only one species participates in the slow step.