a) The first step is finding the molar mass of CH4 to convert the mass given (2.2 g) into moles.
MM = 12.0 + 4*1.0 = 16 g/mol
If 16 g = 1 mole, we can calculate how many moles are 2.2 g by doing the following:
16 g ---- 1 mole
2.2 g ----- x mole
Now we use Avogadro's number to find how many molecules are present in this amount of moles of methane (CH4).
Avogadro's number is 6.0*10^23 molecules/mol
1 mole ---- 6.0*10^23 molecules
0.1375 mole ---- y molecules
There are 8.3*10^22 molecules in 2.2 g of CH4.