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# What is the mass of: (a) 0.2 mole of oxygen atom? (b) 0.5 mole of water molecules?

$$\therefore$$ Mass of 0.2 moles of oxygen atoms = 0.2 × 16 = 3.2u
$$\therefore$$ Mass of 0.5 moles of water molecules = 0.5 × 18 = 9u