The two changes you mentioned have several things in common:
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Chemical Change (for rust): Rust forming on a metal gate is a chemical change, as it involves the reaction of iron with oxygen and moisture to form iron oxide. Although the growth of snail shells is primarily a biological process, it also involves chemical changes as the snails metabolize calcium and other minerals to create their shells.
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Physical Change (for shells): The growth of snail shells is a physical change as it involves the growth and deposition of materials but does not alter the fundamental nature of the materials involved.
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Natural Processes: Both changes occur in nature. Rusting is a natural process that occurs due to environmental conditions, while snails growing shells is part of their biological life cycle.
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Involvement of Elements: Both involve elements found in nature—iron from the metal for rusting and calcium from the environment for building snail shells.
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Slow Changes: Both processes typically occur over a period of time; rust development can take weeks or months depending on conditions, while snails grow their shells gradually over their lifetime.
Choose the relevant points that apply to both changes based on these common characteristics.