To determine the limiting reactant of a reaction, it is important first to know the balanced reaction. For this case, it is:
CH4 + 2O2 = CO2 + 2H2O
We determine as follows:
3.05 mol CH4 (2 mol O2 / 1 mol CH4)= 6.1 mol O2 needed
5.03 mol O2 (1 mol CH4 / 2 mol O2 )= 2.515 mol CH4 needed
Since the needed amount of CH4 is less than what is given, the O2 should be the limiting reactant since it would react completely.
