Final answer:
320 g of oxygen reacted with 120 g of carbon to form 440 g of carbon dioxide, according to the law of conservation of mass.
Step-by-step explanation:
When 120 g of carbon reacts with oxygen to form 440 g of carbon dioxide, we can use the law of conservation of mass to find out the mass of oxygen that reacted. According to the law of conservation of mass, the mass of the reactants will equal the mass of the products. So, the mass of oxygen reacted can be calculated as follows:
Mass of carbon dioxide - Mass of carbon = Mass of oxygen
440 g (mass of CO₂) - 120 g (mass of C) = 320 g of oxygen
This calculation shows that 320 g of oxygen reacted with the carbon to form carbon dioxide.