The molecular weights of $O_2$ and $SO_2$ are $32$ and $64$ respectively. If $1 \, L$ of $O_2$ at $15 \, ^\circ C$ and $750 \, mm$ pressure contains '$N$' molecules,the number of molecules in $2 \, L$ of $SO_2$ under the same conditions of temperature and pressure will be

• A
  $N/2$
• B
  $N$
• C
  $2N$
• D
  $4N$