8g  $O_2$ has same number of molecules as that in :

Number of molecules in 8g  $O_2=\frac{8}{32}\times N_A=\frac{N_A}{4}$
Number of molecules in 14g  $CO=\frac{14}{28}\times N_A=\frac{N_A}{2}$
Number of molecules in 7g  $CO=\frac{7}{28}\times N_A=\frac{N_A}{4}$
Number of molecules in 11g  $C{O}_2=\frac{11}{44}\times N_A=\frac{N_A}{4}$
Number of molecules in 22g  $C{O}_2=\frac{22}{44}\times N_A=\frac{N_A}{2}$