Ethylene difluoride on hydrolysis gives

Major products $A$ and $B$ formed in the following reaction sequence are:

Consider the $S_N1$ solvolysis of the following halides in aqueous formic acid:
$(I)$ $CH_3-CH(CH_3)-CH(Br)-CH_3$
$(II)$ $CH_3-C(CH_3)(Br)-CH_3$
$(III)$ $C_6H_5-CH(Br)-C_6H_5$
$(IV)$ $C_6H_5-CH(Br)-CH_3$
Which one of the following is the correct sequence of the halides given above in the decreasing order of their reactivity?

The reaction of $n$-propyl bromide with ethanolic potassium hydroxide $(KOH)$ produces ...... .

Toluene $\xrightarrow[{heat}]{{NBS\,/\,CCl_4}} A$ $\xrightarrow{{CH_3ONa}} B,$
The final product $(B)$ formed in the reaction sequence is:

What is the number of possible enantiomeric pairs formed during the monochlorination of isopentane?