The formula for water is H2O so there would have to be two Hyrdogens and one oxygen. Therefore it would be 4g of Hydrogen and 16g of Oxygen leaving you with 20g.
The answer is D.
Hope this helps :) ~
The simple formula is C = n/V
n = mols
C = Concentration or Molarity
V = Volume in Liters.
n = 2
V = 4
C = 2 / 4
C = 0.5 mol/Litre
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