Answer:
Atom then element
Step-by-step explanation:
Scientists once thought the most fundamental building block of matter was a particle called the atom. Now we know that the atom is made of many smaller pieces, known as subatomic particles. Every atom contains a central core called the nucleus, made of particles called protons and neutrons.
An element is a pure substance and is made of only one type of atom; it cannot be broken down into a simpler substance.