To find the number of molecules, we'll use the formula:
Number of moles = NumberofmoleculesAvogadronumber
But We were only given the mass of Helium = 11.5g , knowing the atomic mass or molar mass of He = 4 g/mol
Number of moles = massmolarmass = 11.54 = 2.875 moles
Number of molecules = Number of moles x Avogadro number
= 2.875 x 6.02 x 1023
= 17.3075 x 1023
= 1.73 x 1024
