The ${S_{N}2}$ reaction of an asymmetric carbon compound always gives:

Chloropicrin is a strong lachrymatory compound and is used in war. It is prepared by

Sodium tertiary butoxide on reaction with methyl bromide produces the product $P$.
Sodium methoxide upon reaction with tertiary butyl bromide generates the product $Q$.
The products $P$ and $Q$ are

$Ph-CH(Br)-CH_2-CH_2-Br \xrightarrow[\Delta]{Zn-Cu} \text{Product}$. The product of the above reaction is:

The formation of butane nitrile is possible in which of the following reactions?

The increasing order of the reactivity of the following halides for the $S_N1$ reaction is:
$(I)$ $CH_3-CHCl-CH_2-CH_3$
$(II)$ $CH_3-CH_2-CH_2-Cl$
$(III)$ $p-CH_3O-C_6H_4-CH_2Cl$