Yes , the chemist can answer if the compound in K2O or K2O2
The chemical formula and composition of both the compounds is entirely different. The compound K2O2 has an additional molecule of oxygen than K2O and hence will have have higher molecular mass.
In the compound K2O
molecular mass= 2x 39+16 =94
mass ratio of K in compound= 78/94 = 0.830
In the compound K2O2
molecular mass= 2x 39+16X2 =110
mass ratio of K in compound= 78/110 = 0.710
and hence by the required ratio while extracting K , the chemist may know if the compound is K20 or K2O2
If the ratio is anything different from 0.830 and 0.710 then the compund will be something different
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