It is the atom.
Molecules are the smallest part of a substance. Molecules have all the properties of a substance.
The basic unit of matter is an atom. It is also the smallest part of an element that retains all the properties of that element. Since your question ended with an... I would say element fits best.
An atom.
A molecule
That's an atom of gold. An atom is the smallest representative particle of an element.
An atom
The smallest part of matter that retains its own chemical properties is called a(n) _______.
atom
Molecules are the smallest part of a substance. Molecules have all the properties of a substance.
An atom.
It is an atom
Atom
A molecule
The smallest subdivision that retains all of the properties of a molecular compound is a molecule, and the smallest subdivision that retains all of the properties of a ionic compound is a formula unit.
The basic unit of matter is an atom. It is also the smallest part of an element that retains all the properties of that element. Since your question ended with an... I would say element fits best.
The smallest part of an element that still retains its properties is an atom.
The smallest part of an element that has the properties of that element is the atom.