When $tert$-butyl bromide is heated with silver fluoride,the major product obtained is

Reaction $(A)$:
$Ph-CH=CH-CH_3 \xrightarrow[H_2O_2 / OH^-]{B_2H_6 / THF}$ products.
Reaction $(B)$:
$CH_3-CH=CH-Ph \xrightarrow[NaBH_4]{Hg(OAc)_2 / H_2O}$ products.
Correct statement is:

Which of the following is most reactive toward $S_{N}2$ reaction?

The reaction $(CH_3)_3C - Br + H_2O \rightarrow (CH_3)_3C - OH + HBr$ is an example of which type of reaction?

Which one of the following is most reactive towards nucleophilic substitution reaction?

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: