Which of the following undergoes nucleophilic substitution exclusively by $S_N1$ mechanism?

For the following reactions:
$CH_{3}CH_{2}CH_{2}Br + Z^{-} \xrightarrow[substitution]{k_s} CH_{3}CH_{2}CH_{2}Z + Br^{-}$
$CH_{3}CH_{2}CH_{2}Br + Z^{-} \xrightarrow[elimination]{k_e} CH_{3}CH=CH_{2} + HZ + Br^{-}$
where
$Z^{-} = CH_{3}CH_{2}O^{-} (A)$ or $(CH_{3})_{3}CO^{-} (B)$
$k_s$ and $k_e$ are,respectively,the rate constants for the substitution and elimination,and $\mu = \frac{k_s}{k_e}$,the correct option is:

Which among the following is $NOT$ a feature of $S_{N}2$ mechanism?

The product of which of the following reactions undergoes hydrolysis by the $S_N 1$ mechanism?

In the following pairs of halogen compounds,which compound undergoes faster $S_N 1$ reaction?

What is the primary product of an $S_N1$ reaction on an optically active substance?