Consider the following bromides:

The correct order of ${\text{S}}_{\text{N}}1$ reactivity is:

${\text{S}}_{\text{N}}1$ reactivity depends on the stability of the carbocation formed in the rate-determining step.Order of carbocation stability: $3^{\circ }>2^{\circ }>1^{\circ }>\text{Methyl}$.(A) $\text{Me-Br}\to {\text{Me}}^{+}$ (Methyl carbocation)(B) ${\text{Me}}_2\text{CH-Br}\to {\text{Me}}_2{\text{CH}}^{+}$ ($2^{\circ }$ carbocation)(C) ${\text{Me}}_3\text{C-Br}\to {\text{Me}}_3{\text{C}}^{+}$ ($3^{\circ }$ carbocation)Thus, the reactivity order is $C>B>A$.(Note: The options in the original text use Me-Br as Me, but for SN1, the tertiary is always fastest).