$KCN$ reacts readily to give a cyanide with:

Which of the following alkyl halides is most reactive towards the $S_{N}1$ mechanism?

Predict all the alkenes that would be formed by dehydrohalogenation of the following halides with sodium ethoxide in ethanol and identify the major alkene:
$(i)$ $1-$Bromo$-1-$methylcyclohexane
$(ii)$ $2-$Chloro$-2-$methylbutane
$(iii)$ $2,2,3-$Trimethyl$-3-$bromopentane.

Which of the following pairs are correctly matched?
| | Reactants | Products |
|---|---|---|
| $I.$ | $RX + AgOH(aq)$ | $RH$ |
| $II.$ | $RX + AgCN(alc)$ | $RNC$ |
| $III.$ | $RX + KCN(alc)$ | $RNC$ |
| $IV.$ | $RX + Na(ether)$ | $R-R$ |

An alkyl halide $X$ $(C_4H_9Br)$ undergoes nucleophilic substitution by $S_N2$ reaction. The product of $X$ on reaction with $Mg/\text{dry ether}$ followed by $D_2O$ is:

For the reaction:
$RCH_2Br + I^{-} \stackrel{\text{Acetone}}{\longrightarrow} RCH_2I + Br^{-}$
The correct statement is: