The correct option is **B. Electrons occupy distinct energy levels around the nucleus and determine the chemical properties of the atom.** ### Detailed Explanation: 1. **Understanding Atomic Structure**: - An atom consists of a nucleus, which contains protons and neutrons, and electrons that orbit the nucleus. The nucleus is positively charged due to protons, while electrons are negatively charged. 2. **Role of Electrons**: - Electrons are not found in the nucleus; instead, they exist in regions called electron shells or energy levels around the nucleus. These energy levels are quantized, meaning electrons can only exist at specific energy states and not in between. 3. **Energy Levels**: - The arrangement of electrons in these energy levels is crucial. The closest energy level to the nucleus can hold a maximum of 2 electrons, while subsequent levels can hold more (8 in the second level, 18 in the third, etc.). The distribution of electrons across these levels determines how an atom interacts with other atoms. 4. **Chemical Properties**: - The outermost electrons, known as valence electrons, play a significant role in chemical bonding and reactions. Atoms tend to bond with others to achieve a full outer shell, which is often the most stable configuration. This behavior is the foundation of chemical properties and reactivity. 5. **Why Other Options Are Incorrect**: - **A. Electrons are located in the nucleus and contribute to the atomic mass.** - This statement is incorrect because electrons are not located in the nucleus; they orbit around it. Additionally, electrons have a very small mass compared to protons and neutrons, so they do not significantly contribute to the atomic mass. - **C. Electrons are responsible for the gravitational force that holds the nucleus together.** - This statement is misleading. The gravitational force is negligible at the atomic level compared to the electromagnetic force. The nucleus is held together by the strong nuclear force, which acts between protons and neutrons, not electrons. - **D. Electrons are stationary and do not participate in chemical bonding.** - This statement is false. Electrons are not stationary; they are in constant motion within their energy levels. Moreover, they are crucial for chemical bonding, as atoms bond by sharing or transferring electrons to achieve stability. ### Summary of Key Points: - Electrons occupy distinct energy levels around the nucleus, which are quantized. - The arrangement of electrons, especially valence electrons, determines the chemical properties and reactivity of an atom. - Electrons are not located in the nucleus and do not contribute significantly to atomic mass. - The forces that hold the nucleus together are not related to electrons but rather to the strong nuclear force. This understanding of electrons is fundamental in chemistry and physics, as it lays the groundwork for concepts such as chemical bonding, molecular structure, and the behavior of materials.