**Correct Option: C. Electron** ### Detailed Explanation: 1. **Understanding Subatomic Particles**: - Atoms are made up of three main subatomic particles: protons, neutrons, and electrons. - **Protons** are positively charged particles found in the nucleus of an atom. - **Neutrons** are neutral particles (no charge) also located in the nucleus. - **Electrons** are negatively charged particles that orbit the nucleus in various energy levels or shells. 2. **Role of Electrons in Chemical Properties**: - The chemical properties of an atom are primarily determined by its electrons, particularly the electrons in the outermost shell, known as valence electrons. - These valence electrons are involved in chemical bonding and reactions. They determine how an atom interacts with other atoms, which is the essence of chemistry. - For example, atoms with a full outer shell (like noble gases) are generally inert and do not react chemically, while atoms with one or more unpaired valence electrons (like alkali metals) are highly reactive. 3. **Chemical Bonds**: - Atoms can form bonds with other atoms through the sharing (covalent bonds) or transfer (ionic bonds) of electrons. - The type and number of bonds an atom can form, as well as its reactivity, are dictated by the arrangement and number of its valence electrons. 4. **Why Other Options Are Incorrect**: - **A. Neutron**: Neutrons contribute to the mass of the atom and help stabilize the nucleus, but they do not influence chemical properties or reactivity. They do not participate in chemical bonding. - **B. Proton**: While protons determine the identity of the element (the atomic number), they do not directly influence how the atom interacts chemically. The number of protons affects the number of electrons in a neutral atom, but it is the electrons that dictate chemical behavior. - **D. Nucleus**: The nucleus, which contains protons and neutrons, is the central part of the atom and does not directly participate in chemical reactions. It is the electrons surrounding the nucleus that are responsible for chemical properties. ### Summary of Key Points: - **Electrons determine chemical properties**: The arrangement and number of valence electrons dictate how an atom interacts with others. - **Chemical bonding**: Electrons are involved in forming bonds, which are crucial for chemical reactions. - **Protons and neutrons**: While they are essential for defining the atom's identity and stability, they do not influence chemical behavior. - **Nucleus**: The nucleus is important for the atom's structure but does not participate in chemical reactions. ### Revision Summary: - The **electron** is the subatomic particle that determines the chemical properties of an atom. - **Valence electrons** are key in chemical bonding and reactivity. - **Protons** define the element but do not affect chemical behavior. - **Neutrons** stabilize the nucleus but are not involved in chemical reactions.