The mass of oxygen that is required to react completely with 2 moles of CH4 is 128 grams
calculation
mass = moles xmolar mass
The molar mass of O2= 16 x2 = 32 g/mol
find the number of moles
first write the the equation for reaction
CH4 + 2O2 → CO2 + 2H2O
the mole ratio between CH4 to O2 is 1:2 therefore the moles of O2 = 2 x2 = 4 moles
mass is therefore = 32 g/mol x 4 moles = 128 grams
