RISE Science Grade 8 Practice Questions - RISE Science - Grade 8 Exam

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An iron nail with a mass of 5.0 grams is left in a humid environment for several weeks. When re-weighed, the rusty nail has a mass of 5.7 grams. Why did the mass of the solid nail increase?

Iron atoms multiplied inside the nail due to exposure to water. Oxygen gas from the surrounding air chemically bonded with iron atoms to form rust. The nail absorbed heat energy which added extra mass to the solid metal. Rust is denser than pure iron, so the nail gained weight without adding atoms.

Correct Answer:

Oxygen gas from the surrounding air chemically bonded with iron atoms to form rust.

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