What is the density of water vapour at the boiling point of water?

• A
  $1 \times 10^{-4} \ g \ cm^{-3}$
• B
  $1 \ g \ cm^{-3}$
• C
  $6 \times 10^{-4} \ g \ cm^{-3}$
• D
  $4 \times 10^{-4} \ g \ cm^{-3}$