Firstly, the formula of water is H2O. There is 1 mole of oxygen atoms per mole of water. Therefore, in 4.2 moles of water there are 4.2 moles of oxygen atoms. The real amount is calculated as follows:
[tex]4.2 \times 6.02 \times {10}^{23} = [/tex]
[tex] = 2.5284 \times {10}^{24} [/tex]
