$S_N1$ reactions are generally carried out in which type of solvents?

Consider the reactions:
$(i) \ (CH_3)_2CHCH_2Br \xrightarrow{C_2H_5OH} (CH_3)_2CHCH_2OC_2H_5 + HBr$
$(ii) \ (CH_3)_2CHCH_2Br \xrightarrow{C_2H_5O^-} (CH_3)_2CHCH_2OC_2H_5 + Br^-$
The mechanisms of reaction $(i)$ and $(ii)$ are respectively:

Among the following,the compound which undergoes the fastest solvolysis is

The correct order of $C-X$ bond polarity is:

Compare the rate of $E_2$ reaction for the following compounds:
$a$: $(CH_3)_3C-Br$
$b$: $CH_3-CH(Br)-CH_3$
$c$: $CH_3-CH_2-Br$

Which among the following will have the highest density?