**Correct Option: B. Atoms consist of a nucleus made of protons and neutrons, surrounded by a cloud of electrons.** ### Detailed Explanation: 1. **Understanding Atomic Structure**: - An atom is the basic unit of matter and is composed of three primary subatomic particles: protons, neutrons, and electrons. - The **nucleus** is at the center of the atom and contains protons (which are positively charged) and neutrons (which have no charge). The number of protons in the nucleus defines the element (e.g., hydrogen has 1 proton, carbon has 6 protons). - Surrounding the nucleus is a region known as the **electron cloud**, where electrons (which are negatively charged) are found. These electrons occupy various energy levels or orbitals around the nucleus. 2. **Why Option B is Correct**: - Option B accurately describes the structure of an atom by highlighting the nucleus's composition (protons and neutrons) and the presence of electrons in a cloud around it. This model is supported by extensive experimental evidence, including Rutherford's gold foil experiment, which demonstrated that atoms have a dense nucleus surrounded by a larger volume of space where electrons reside. 3. **Why the Other Options are Incorrect**: - **Option A**: "Atoms are composed of protons and electrons only, with neutrons being irrelevant." - This statement is incorrect because it ignores the presence of neutrons, which play a crucial role in the stability of the nucleus. Neutrons help to bind protons together in the nucleus, counteracting the repulsive forces between the positively charged protons. Without neutrons, many atomic nuclei would be unstable. - **Option C**: "Atoms are indivisible particles that cannot be broken down into smaller components." - This statement is outdated. While atoms were once thought to be indivisible, we now know that they can be broken down into smaller particles (protons, neutrons, and electrons). Furthermore, protons and neutrons themselves are made up of quarks, which are even smaller particles. Thus, this option does not accurately reflect modern atomic theory. - **Option D**: "Atoms contain only positively charged particles, with no negative charges present." - This statement is incorrect because it completely disregards the existence of electrons, which are essential to the structure of an atom. Electrons are fundamental to chemical bonding and the overall charge balance of atoms. In a neutral atom, the number of protons (positive) equals the number of electrons (negative), resulting in no overall charge. ### Summary of Key Points: - Atoms consist of a nucleus made of protons and neutrons, surrounded by a cloud of electrons. - Neutrons are essential for the stability of the nucleus and cannot be ignored. - Modern atomic theory recognizes that atoms can be divided into smaller components, contrary to the idea of indivisibility. - Electrons are crucial for the charge balance and chemical properties of atoms. ### Revision Summary: - Atoms are made of protons, neutrons, and electrons. - The nucleus contains protons and neutrons; electrons form a cloud around it. - Atoms can be divided into smaller particles, contrary to earlier beliefs. - Electrons are essential for the atom's charge and chemical behavior.