There is 1 O atom in 1 H2O molecule thus there are 12 O atoms in 12 H2O molecules.
4 moles of oxygen atoms (being present in 4 moles of H2O) and, so: 4 moles of oxygen atoms is 4*6.02*1023 = 24.1*1023 molecules ATOMS of oxygen
4 moles of oxygen atoms are present in 4 moles of H2O
2 Hydrogen atoms are in water and 1 oxygen atom
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