To make the conversion that they ask us, we must take into account that a mole of any substance has 6.022x10^23 molecules, that is Avogadro's number. So the molecules contained in 1.75mol of H2O will be:
[tex]\begin{gathered} MoleculesH_2O=GivenmolH_{2O}\times\frac{6.022\times10^{23}molecules}{1molH_2O} \\ MoleculesH_2O=1.75molH_{2O}\times\frac{6.022\times10^{23}molecules}{1molH_2O} \\ MoleculesH_2O=1.05\times10^{24}moleculesH_2O \end{gathered}[/tex]In 1.75 mol of H2O there are 1.05x10^24 molecules of H2O
