The smallest particle of a substance that retains all the properties of that substance and is composed of one or more atoms is called a molecule.

Here's why:

* Smallest Particle: Molecules are the smallest units of a substance that can exist independently and still retain the chemical properties of that substance.

* Retains Properties: A molecule of water (H₂O) will have the same properties as a large body of water – it will be a liquid at room temperature, have a specific density, and be capable of dissolving certain substances.

* One or More Atoms: Molecules are made up of two or more atoms chemically bonded together. For example, a water molecule is made of two hydrogen atoms bonded to one oxygen atom.

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