Select whether the following combinations of reactants will react by substitution ($S_{N}1,S_{N}2$ or elimination ($E_1,E_2$ mechanism).

The correct option is A $S_{N}1$
The carbocation formed in first step in first step is $2^o$ which rearrange itself to $3^o$ carbocation which is more stable than $2^o$ carbocation due to hyperconjugation effect. So, the reaction followed $S_{N}1$ mechanism.
Mechanism:-