How much oxygen is theoretically required for the complete combustion of 13.44 liters of methane?

Let us write the equation of the methane combustion process:
СН4 + 2О2 = СО2 + 2Н2О + Q – heat, carbon dioxide and water are released;

Determine the amount of starting materials based on the proportion:
1 mole of gas – 22.4 liters

X mol (CH4) – 13.44 L from here, X mol (CH4) = 1 * 13.44 / 22.4 = 0.6 mol.

0.6 mol (CH4) – X mol (O2);

-1 mol -2 mol from here, X mol (O2) = 0.6 * 2/1 = 1.2 mol.

We find the volume of O2:
V (O2) = 1.2 * 22.4 = 26.88 L

Answer: to burn methane, you will need oxygen with a volume of 26.88 liters.