That is a pure substance that consists of the base particle and atomic number is the number of protons in the nucleus of the element. For example, oxygen, carbon, aluminium
That is pure substance consisting of elementary particles, atomic number. As the number of protons in the nucleus, for example, carbon, oxygen, aluminum.
The element is a compound which is composed of elementary particles atomic number. The number of protons in the nucleus of the element, for example, carbon, oxygen, aluminium