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Well, one mole of h20 weighs 18.015 grams (1 oxygen is 15.999+2 hydrogen at 1.008 each). So in 30 grams, there are 1.665 moles (30/18.015). Now, oxygen has 8 electrons and hydrogen has 1 electron each. So there are 10 electrons in each molecule, and there are 1.665 moles of molecules, so you get 16.65 moles of electrons. Multiply that by 6.022 x 10^23 and you get 1.002 x 10^25 electrons