Usage - Pronoun-Antecedent Agreement. A pronoun is a word used to stand for (or take the place of) a noun. A word can refer to an earlier noun or pronoun in the sentence. Example:
A subatomic particle is a unit of matter or energy that's the fundamental makeup of all matter. According to modern atomic theory, an atom has a nucleus, which is its center, or core. The nucleus contains subatomic particles: protons and neutrons. Protons are positively-charged particles. Neutrons are neutral particles.
All atoms have a dense central core called the atomic nucleus. Forming the nucleus are two kinds of particles: protons, which have a positive electrical charge, and neutrons, which have no charge. All atoms have at least one proton in their core, and the number of protons determines which kind of element an atom is. For example, an oxygen atom has 8 protons.