What is the difference between an atom and a compound?

An atom cannot be broken down any smaller whereas a compound is made up of atoms and can be broken down into smaller pieces (the individual atoms that make it up)
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A molecule is formed when two or more atoms join together chemically. A compound is a molecule that contains at least two different elements. All compounds are molecules but not all molecules are compound. The smallest bit of each of these substances would be referred to as a molecule.

The answer should be c.

Noble gases is far right