Answer:
20%
Explanation:
molecular formula of deuterium oxide, or "heavy water" is [tex]D_2O[/tex]
molecular weight of D2= 4.028204 g/mol
molecular weight of oxygen= 16 g/mol
therefore, molecular weight of water = 20.028204 g/mol
therefore, the percent hydrogen (by mass) in a "heavy water" molecule
=(molecular weight of D2/molecular weight of water)
[tex]= \frac{4}{20.028204}\times100[/tex]
= 20%