Question

when 21.6g of carbon were burned in the presence of 73.9g of oxygen 16.3g of oxygen remain unreacted. What mass of carbon dioxide was produced

Answer 1

If some O2 remains unreacted, then C is the limiting reagent.
mols C = grams/atomic mass = ?
Using the coefficients in the balanced equation, convert mols C to mols CO2.
Now convert mols CO2 to grams. g = mols x molar mass