Answer:
When carbon is heated in air, it undergoes a process known as combustion or burning. During this process, carbon reacts with oxygen present in the air, resulting in the production of carbon dioxide gas. This reaction causes the carbon atoms to be lost in the form of carbon dioxide molecules. Hence, the original mass of carbon decreases due to the formation of lighter carbon dioxide molecules that are released into the atmosphere. Overall, the burning of carbon in air results in a reduction in its mass.