Does an iron nail gain mass or lose mass when it rusts (a form of burning)?

When an iron nail rusts, it gains mass. This process involves the chemical reaction between iron, oxygen, and moisture in the environment, resulting in the formation of iron oxide (rust). The added mass comes from the oxygen in the air and water that combine with the iron, leading to an increase in the total mass of the rusted nail. Thus, the overall mass of the nail increases as it rusts.