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

An 'Assertion' $(A)$ and a 'Reason' $(R)$ are given below. Choose the correct answer from the following options.
Assertion $(A)$: Vinyl halides do not undergo nucleophilic substitution easily.
Reason $(R)$: Even though the intermediate carbocation is stabilized by loosely held $p-$ electrons,the cleavage is difficult because of strong bonding.

Which compound in each of the following pairs will react faster in $S_N2$ reaction with $OH^{-}$?
$(i)$ $CH_3-Br$ or $CH_3-I$
$(ii)$ $CH_3-C(CH_3)_2-Cl$ or $CH_3-Cl$

$Cl-CH_2-C(CH_3)_2-CH_2-CH_2-Cl + I^- \xrightarrow[DMF]{} \text{product}$; The major product of this reaction is:

Which of the following compounds has the lowest boiling point?

Identify $A$ and $B$ in the chemical reaction.