How many molecules are in 30 liters of methane

 Pv=nrt. We want to find N, which is the number of mols, so that we can later turn it into molecules, thus, we are going to use this formula: n=Pv/rt.
Pressure=100,000
Volume= 0.03 because 30 liters is the same as 30dm^3
R= 8.31 (remember this number is always constant)
Temperature= 273k

n= 100,000 x 0.03/8.31 x 273
n= 1.322383994
n= 1.322383994 x 6.022 x 10^23 < (Avogadro's number.)
7.964 x 10^23  < This is your answer!