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.
Location of Protons. Protons are positively charged particles within atoms. Each atom has at least one proton; in fact, the number of protons determines the identity of the atom. Protons reside in the nucleus of the atom, which might seem strange since they are positively charged and thus repel each other.