Ethyl bromide gives ethylene when reacted with

The reaction of $4-$bromobenzyl chloride with sodium cyanide in ethanol leads to the formation of

Identify the correct order of reactivity for the $E_2$ reaction with alcoholic $KOH$ for the following compounds:
$(i)$ $(CH_3)_3C-Cl$
(ii) $(CD_3)_3C-Cl$
(iii) $(CT_3)_3C-Cl$

Consider the following reaction:
(Cyclohexyl)methyl chloride + $CH_3ONa$ $\rightarrow$ $1-$(methoxymethyl)cyclohex$-1-$ene.
The mechanism of the reaction will be:

The following compound on hydrolysis in aqueous acetone will give:

Haloalkanes react with $KCN$ to form alkyl cyanides as the main product,while $AgCN$ forms isocyanides as the chief product. Explain.