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

Which one is a nucleophilic substitution reaction among the following?

The product obtained from the reaction is:

The rate of $S_{N}2$ reaction is:

Under the specified conditions,substrate $X$ undergoes substitution and elimination reactions to give products $A - D$. $A$ and $B$ are stereoisomers,but not enantiomers. $C$ and $D$ are enantiomers. $A$ is not an isomer of $C$. Which of the following could be the starting material $X$ ?
$X \xrightarrow[\Delta]{H_2O} A + B + C + D$

Major product of the reaction is :