This is the 5206th most frequent Japanese word.
陽子
"陽子" means "proton" in English.
陽子 in this context refers to 'proton', which is a scientific term for a subatomic particle.
陽子は原子の構成部分である。
A proton is a component of an atom.
陽子 here is used as a proper noun referring to a person's name, specifically 'Yoko'.
陽子さんはとても優しい人です。
Yoko is a very kind person.
陽子 again represents the name 'Yoko', denoting the person whose research is being discussed.