Best definition of an atom?

Don't trust them

Explanation:

They make up everything

Answer: An atom is a particle of matter that uniquely defines achemical element.

Explanation: An atom is a particle of matter that uniquely defines a chemical element. An atom consists of a central nucleus that is usually surrounded by one or more electrons. Each electron is negatively charged. The nucleus is positively charged, and contains one or more relatively heavy particles known as protons and neutrons.