What particles are contained within the nucleus of an atom?

The nucleus of an atom is composed of protons and neutrons, collectively known as nucleons. Protons are positively charged particles, while neutrons are neutral. The presence of these two types of particles in the nucleus contributes to the majority of an atom's mass and plays a crucial role in determining the chemical properties of an element.

The arrangement of protons in the nucleus also defines the atomic number, which identifies the element on the periodic table. Neutrons contribute to the stability of the nucleus by offsetting the repulsive forces between the positively charged protons. This balance is essential for the integrity of the atom.

Other options list particles that are not found in the nucleus. For example, electrons orbit the nucleus and are not part of it, while positrons are the antimatter counterparts of electrons and do not exist in a stable state within the nucleus. Thus, the correct identification of protons and neutrons as the constituents of the nucleus captures the fundamental structure of atomic matter.