Which of the following,on heating with aqueous $KOH$,produces acetaldehyde?

Which of the following is an example of an $S_N2$ reaction?

Consider the following bromides.
The correct order of $S_N1$ reactivity is

The organic halide,which does not undergo hydrolysis by $S_{N}1$ mechanism is

When alcoholic $KOH$ is reacted with $CH_3CH_2Cl$ to form an alkene,which species acts as the attacking reagent?

Identify the correct order of reactivity for the reaction with alcoholic $KOH$ for the following compounds:
$(a)$ $2$-bromo-$2,3$-dimethylbutane
$(b)$ $2$-chlorobutane
$(c)$ $2$-bromobutane
$(d)$ $1$-bromopropane