The number of non-polar molecules from the following is __________ . \( \mathrm{HF}, \mathrm{H_2O}, \mathrm{SO_2}, \mathrm{H_2}, \mathrm{CO_2}, \mathrm{CH_4}, \mathrm{NH_3}, \mathrm{HCl}, \mathrm{CHCl_3}, \mathrm{BF_3} \)