What is $A$ in the following reaction?
$3\text{-iodobenzyl chloride} \xrightarrow{NaCN, DMF} A$

Arrange the following compounds in decreasing order of the rate of electrophilic addition reaction:
$(P)$ $p$-vinylbenzaldehyde
$(Q)$ $p$-vinylanisole
$(R)$ $p$-methylstyrene
$(S)$ $p$-dimethylaminostyrene

What is the major product formed in the following reaction?

Among the following organic halides,arrange them in the increasing order of their dehydrohalogenation reactions in the presence of alcoholic $KOH$:
$(A)$ $CH_3-CH_2-Br$
$(B)$ $CH_3-CH_2-CH_2-Br$
$(C)$ $CH_3-CH(Br)-CH_3$
$(D)$ $(CH_3)_3-CBr$

The major product of the following reaction is:
$C_6H_5-CH_2-C(Br)(CH_3)-CH_2-CH_3 \xrightarrow[C_2H_5OH]{C_2H_5ONa}$

What is formed when $1$-bromo-$3$-chlorocyclobutane is treated with $2$ equivalents of sodium in ether?