Question: how many grams of oxygen are needed to complete the combustion of 8 grams of methane ch4?
Answer: CH4+2O2======>CO2+2H20. So 1 mole of methane requires 2 moles of oxygen for complete combustion. So 16 g of Methane requires 64 g of oxygen for the complete combustion. So 8 g of Methane requires = 8x64/16=32 g of oxygen.