Number of molecules from the following which are exceptions to octet rule is ______.
\( \mathrm{CO_2} \), \( \mathrm{NO_2} \), \( \mathrm{H_2SO_4} \), \( \mathrm{BF_3} \), \( \mathrm{CH_4} \), \( \mathrm{SiF_4} \), \( \mathrm{ClO_2} \), \( \mathrm{PCl_5} \), \( \mathrm{BeF_2} \), \( \mathrm{C_2H_6} \), \( \mathrm{CHCl_3} \), \( \mathrm{CBr_4} \)
