Chemistry
posted by annabel .
How many moles of O2 are needed for the complete combustion of 3 moles of CH4?

Write and balance the equation, then use the coefficients.
CH4 + 2O2 ==> CO2 + 2H2O
The equation tells you that 1 mol CH4 requires 2 mols O2; therefore, 3 mols CH4 will require......mols O2.