How many moles are there in 40 g of He?

Molar mass of Helium = 4g

The given mass of Helium = 40g

Thus the number of moles of Helium =    $\frac{\mathrm{Given} \mathrm{mass} \mathrm{of} \mathrm{a} \mathrm{substance}}{\mathrm{Molecular} \mathrm{mass} \mathrm{of} \mathrm{a} \mathrm{substance}}$

                                                                          =     $\frac{40}{4}$

Moles present in 40 g of He  = 10 moles