Calculate the mass percentage of oxygen present in the following compounds and state the law of chemical combination associated.
Given, H=1,O=16

(1)Water (H2O)
(2) Hydrogen peroxide (H2O2)

Dear student ,
(1)  atomic mass of H = 1 and O = 16 gm / mol
   Molar mass of H₂O =  2 H + O = 2 + 16 = 18 gm / mole 
  Mass % of O in H₂O =  $$\begin{gathered} \frac{mass of oxygen}{mass of water }\times 100 \\ =\frac{16}{18} \times 100 \end{gathered}$$
                                         =  88.89 % 
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