Calculate the number of molecules in 4 g of methane.
[Atomic mass of C = 12 u and H = 1 u]
Molar mass of methane = 12 + 4 X 1 = 16gmol~1
16 g of CH4 contains 6.022 X ${10}^{23}$ molecules
4g of methane will contain 6.022 X ${10}^{23}$ x 4 / 16
= 1.5055 x ${10}^{23}$ molecules