The number of non-polar molecules from the following is
$\mathrm{HF},{\mathrm{H}}_2\mathrm{O},{\mathrm{SO}}_2,{\mathrm{H}}_2,{\mathrm{CO}}_2,{\mathrm{CH}}_4,{\mathrm{NH}}_3,\mathrm{HCl},{\mathrm{CHCl}}_3,{\mathrm{BF}}_3$

The molecules which have perfect geometry and no lone pairs are zero dipole moment molecules. Those molecules termed as non-polar molecules. Amongst the given compounds, ${\mathrm{CH}}_4, {\mathrm{CO}}_2,{\mathrm{H}}_2,{\mathrm{BF}}_3$ are non polar molecules.

${\mathrm{H}}_2\mathrm{O}$ has two lone pairs and two bond pairs. ${\mathrm{SO}}_2$ has two sigma bond pairs and one lone pair. ${\mathrm{CHCl}}_3$ has net dipole moment because the bond moments do not cancel with each other. ${\mathrm{NH}}_3$ have one lone pair and three bond pairs. In $\mathrm{HF}$ bond moment is the dipole moment. Hence, all these molecules have some net dipole moment.

The non-polar molecules are ${\mathrm{CO}}_2, {\mathrm{H}}_2, {\mathrm{CH}}_4$ and ${\mathrm{BF}}_3$