Of the five isomeric hexanes, the isomer which can give two monochlorinated compounds is

Of the isomeric hexanes, the isomers that give the minimum and maximum number of monochloro derivatives are respectively

n-Hexane on heating to $773 \mathrm{K}$ at $10-20$ atmospheric pressure in the presence of oxides of vanadium supported over alumina, yields

$\mathrm{n}-{\mathrm{C}}_7{\mathrm{H}}_{16}\underset{10-20\mathrm{atm}}{\overset{{\mathrm{V}}_2{\mathrm{O}}_5, 500°\mathrm{C}}{\to }}\mathrm{A}\stackrel{{\mathrm{Cl}}_2, \mathrm{h\nu }}{\to }\mathrm{B}$

What is B in the above reaction?