How many H atoms present in 72grams of H2O?
72 grams of water has 4 moles. As every water molecule has two hydrogen atoms, there are 8 moles of hydrogen atoms. It is equivalent to 4.818 x 1024 atoms.
5 moles H2O (1 mole O/1 mole H2O)(6.022 X 1023/1 mole O)(1 mole O atoms/6.022 X 1023) = 5 moles oxygen atoms =================( as you see this is a formal set up that you do not need to use fully as Avogadro's number is over itself as a form of one ) 5 moles H2O (2 moles H/1 mole H2O)6.022 X 1023/1 mole H)(1 mole H atoms/6.022 X 1023) = 10 moles hydrogen atoms ====================