The number of monochlorination products are formed by an alkane with one neo Carbon atom and whose molecular mass is 72.

General formula of alkane is ${\mathrm{C}}_{\mathrm{n}}{{\mathrm{H}}_2}_{\mathrm{n}+2}$

$\therefore 12\mathrm{n}+2\mathrm{n}+2=72$

Molecular formula is ${\mathrm{C}}_5{\mathrm{H}}_{12}$ i.e. neo-pentane

it gives only one monochlorinated products.