Which of the following halogens reacts explosively with alkanes?

$A$ solution of $D(+)-1-$chloro$-1-$phenylethane in toluene racemises slowly in the presence of a small amount of $SbCl_5$,due to the formation of:

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

The chlorine atom of the following compound that reacts most readily with $AgNO_3$ to give a precipitate is

Identify the major product for the following reaction:
$1$-fluoro-$1$-methylcyclohexane $\xrightarrow[\Delta]{Alc. KOH}$ ?

$CH_3-CH_2-Cl \xrightarrow{alc. KOH} A$,the product is