Rust results from iron’s reaction to oxygen. An iron nail gains mass when it rusts. How does this reaction support the law of conservation of mass?

When iron rusts, it combines chemically with oxygen from the air. The rusted nail’s mass includes both the original iron and the oxygen that joined it, so the total mass is conserved when all reactants are counted. Choice C correctly states that the rust’s mass equals the mass of the iron and the oxygen that reacted with it.

AI-written and checked against the verified answer.