The correct answer is option 1 - kg. When 1 kg of carbon is heated, it produces 1 kg of CO2. This is because the atomic weight of carbon is 12, and the atomic weight of oxygen (found in CO2) is 16. Therefore, the molecular weight of CO2 is 12 + 16 + 16, which is equal to 44. Since the atomic weight of carbon is 12, heating 1 kg of carbon produces 1 kg of CO2. It is important to note that the question specifies the heating of carbon, not any other compound or substance containing carbon. If the heating process involves a different substance or compound, the amount of CO2 produced would differ.