Which alkyl halide undergoes the ${S}_{N}1$ reaction most rapidly?

Among $CH_3F$,$CH_3Cl$,$CH_3Br$,and $CH_3I$,which one does not give methane on reduction?

The major product obtained when this substrate is subjected to $E_2$ reaction under the treatment of potassium $tert$-butoxide is:

Choose the false statement from the following about $S_N1$ reaction mechanism.

Explain the stereochemistry of $S_{N}1$ reaction with a suitable example.

For the reactions given below:
$(I)$ Cyclohexyl chloride $\rightarrow$ Cyclohexyl cation + $Cl^-$,$\Delta H_1^{\circ}$
$(II)$ Cyclohex$-2-$enyl chloride $\rightarrow$ Cyclohex$-2-$enyl cation + $Cl^-$,$\Delta H_2^{\circ}$
$(III)$ Benzyl chloride $\rightarrow$ Benzyl cation + $Cl^-$,$\Delta H_3^{\circ}$
$(IV)$ Chlorobenzene $\rightarrow$ Phenyl cation + $Cl^-$,$\Delta H_4^{\circ}$
The correct decreasing order of enthalpies of reaction for producing the carbocation is: