Why is a shell considered to be biotic​

In biology, a shell is defined as a protective structure of mollusks and crustaceans. A shell is considered to be biotic because it came from something living. Shells are not in fact alive as they are made of calcium carbonate and in some cases α-chitin, two non living materials

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acids are substances that ionize (break off) in an aqueous solution to produce hydrogen (h+) ions

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