What is obtained when nitric acid reacts with chloroform?

In the following reaction sequence,the correct structure$(s)$ of $X$ is (are)
$X$ $\xrightarrow[2) NaI, Me_2CO]{1) PBr_3, Et_2O}$ $\xrightarrow{3) NaN_3, HCONMe_2} \text{enantiomerically pure product}$

Which of the following compounds has the highest reactivity towards $S_N2$ reaction?

The major product $(A)$ is:

The order of relative reactivity of the given halides towards $S_N2$ reaction is :

Formation of $2-$butene from $2-$bromobutane is according to