Final answer:
The nail seems larger and heavier because it has reacted with oxygen in the environment (oxidation), making it appear so, but this does not violate the law of conservation of mass. The mass that appears to be gained is from the oxygen atoms from the air adhering to the original metal of the nail. The total mass of the system (nail plus oxygen) remains constant, in accordance with the conservation of mass.
Step-by-step explanation:
The observation that a nail left outside seems larger and heavier does not disprove the law of conservation of mass. Option A suggests absorption which is plausible, but the core reason aligns with option C. When the nail is left outside, it can undergo a chemical reaction known as oxidation, where the metal reacts with oxygen in the air to form metal oxide. This process can make the nail appear larger and heavier due to the addition of oxygen atoms to the metal's structure. This is closely analogous to the experiment by Antoine Lavoisier who demonstrated the conservation of mass with the reaction of tin in a sealed flask.
The correct answer is that the nail has undergone a chemical reaction, causing an apparent increase in mass, but in reality, it just combined with oxygen from the environment. In terms of the law of conservation of mass, the total mass before and after the chemical reaction is in fact conserved, as the increase in the nail's mass is exactly balanced by the mass of the oxygen that has reacted with it.
In Lavoisier's experiments, whether it was burning wood or reacting magnesium with oxygen in a sealed flask, the mass remained constant after the reaction when accounting for all components. If a nail absorbs moisture or dust, those would be external factors and not a direct part of the chemical reaction, although they could contribute to a perceived change in mass.