Final answer:
An atom is composed of a nucleus containing protons and neutrons, and an outer region containing electrons in orbit around the nucleus.
Step-by-step explanation:
An atom is composed of two regions: the nucleus, which is in the center of the atom and contains protons and neutrons, and the outermost region of the atom which holds its electrons in orbit around the nucleus. Atoms contain protons, electrons, and neutrons, among other subatomic particles. The only exception is hydrogen (H), which is made of one proton and one electron with no neutrons.