The total number of molccules with zero dipole moment among CH 4 , BF 3 , H 2 O , HF , NH 3 , CO 2 and SO 2…

Dipole moment:- The polarity of a covalent bond can be conveniently measured in terms of a physical quantity called dipole moment. The dipole moment is the vector sum of all the bond moments. The molecules with perfect geometries with zero lone pairs have zero dipole moment.

Amongst the given compounds, 

${\mathrm{CO}}_2, {\mathrm{BF}}_3, {\mathrm{CH}}_4$ have zero dipole moments.