If you are talking about individual atoms, it is hydrogen by mass or helium by radius.
The smallest quantity of an element is an atom.
a quark or if you mean the smallest element hydrogen
ATOM
the smallest element is hydrogen of which its valency is one.
The atom is the smallest unit of an element that has all the properties of the element.
The smallest identifiable unit of an element that retains the properties of the element is an atom.
The smallest particle of an element is called an atom.
An atom is the smallest particle that is still recognisably the element
a pixel is the smallest element in an electronic image
atom is the smallest part of element
The smallest unit of a chemical element is the atom.
If an element were broken down into its smallest particles, you would get atoms of that element. Each atom is the smallest unit of an element that retains the properties of that element.