In the chlorination of ethane in the presence of sunlight which one of the following is also formed in minute quantity ?        

The reactions that are involved in sunlight occur via radical formation. It is an chain reaction. In the chlorination of ethane under sunlight produces chlorine radical as well as ethyl radical. Chlorine radical combine with ethyl radical produces ethyl chloride. If ethyl radical combine itself produces butane as minor product.

Initiation: ${\mathrm{Cl}}_2+\mathrm{hv}\to 2{\mathrm{Cl}}^{.}$

Propagation:   ${\mathrm{Cl}}^{.}+{\mathrm{C}}_2{\mathrm{H}}_6\to {\mathrm{C}}_2{{\mathrm{H}}_5}^{.}+\mathrm{HCl}$

${\mathrm{C}}_2{{\mathrm{H}}_5}^{.}+{\mathrm{Cl}}_2\to {\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}+{\mathrm{Cl}}^{.}$ 

Termination: ${\mathrm{Cl}}^{.}+{\mathrm{Cl}}^{.}\to {\mathrm{Cl}}_2$ 

${\mathrm{C}}_2{{\mathrm{H}}_5}^{.}+{\mathrm{C}}_2{{\mathrm{H}}_5}^{.}\to {\mathrm{C}}_4{\mathrm{H}}_{10}$ 

${\mathrm{C}}_2{{\mathrm{H}}_5}^{.}+{\mathrm{Cl}}^{.}\to {\mathrm{C}}_2{\mathrm{H}}_5\mathrm{Cl}$

Hence the correct option is (B).