To calculate the molecules present in the given moles we will apply for Avogadro's number. Avogadro's number tells us that in one mole of any substance there are 6.022x10^23 molecules.
Therefore if we have 4 moles of NaCl we will have:
[tex]\begin{gathered} moleculesNaCl=GivenmolNaCl\times\frac{6.022\cdot10^{23}moleculesNaCl}{1molNaCl} \\ moleculesNaCl=4molNaCl\times\frac{6.022\cdot10^{23}moleculesNaCl}{1molNaCl} \\ moleculesNaCl=2\times10^{24}moleculesNaCl \end{gathered}[/tex]In 4 moles of NaCl there are 2 x10^24 molecules