The total number of molecules with zero dipole moment among \( \mathrm{CH_4} \), \( \mathrm{BF_3} \), \( \mathrm{H_2O} \), \( \mathrm{HF} \), \( \mathrm{NH_3} \), \( \mathrm{CO_2} \) and \( \mathrm{SO_2} \) is __________.