The equation for the reaction is is 2H2O = 2H2 + O2
Ratio of H to O in water = 2:1
Molar mass of water = 2*1.008 + 15.999 = 18.015
18.015 g gives 2*1.008 hydrogen
20 gives 2* 1.008 * 20 / 18.015
= 2.24 g hydrogen to the nearest hundredth.
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