The reaction $CH_4 + Cl_2 \xrightarrow{uv \ light} CH_3Cl + HCl$ is an example of

$A$ hydrocarbon of molecular mass $72 \ g \ mol^{-1}$ gives a single monochloro derivative and two dichloro derivatives on photochlorination. Give the structure of the hydrocarbon.

Identify the major product $Y$ in the following reaction sequence:
$CH_3-CH(CH_3)-CH_2-Cl$ $\xrightarrow[\text{dry ether}]{Na} X$ $\xrightarrow[\text{monobromination}]{Br_2/h\nu} Y$ (major)

Determine the number of mono-chloro products (structural isomers only) formed by the reaction of isopropylcyclopentane with $Cl_2/\Delta$.

The main constituent of marsh gas is:

$Br^{\bullet}$ will abstract which of the hydrogen most readily?