Which of the following pairs of gases contains the same number of molecules?

• A
  $16 \ g$ of $O_2$ and $14 \ g$ of $N_2$
• B
  $8 \ g$ of $O_2$ and $22 \ g$ of $CO_2$
• C
  $28 \ g$ of $N_2$ and $22 \ g$ of $CO_2$
• D
  $32 \ g$ of $O_2$ and $32 \ g$ of $N_2$