The correct option is **B. A pure substance made up of only one type of atom that cannot be chemically broken down.** ### Detailed Explanation: 1. **Definition of an Element**: - In chemistry, an element is defined as a pure substance that consists entirely of one type of atom. This means that all the atoms in an element have the same number of protons in their nuclei, which is known as the atomic number. For example, all carbon atoms have 6 protons, making carbon an element. 2. **Indivisibility of Elements**: - Elements cannot be broken down into simpler substances by chemical means. This is a fundamental characteristic of elements. While they can undergo physical changes (like melting or boiling), their chemical identity remains intact. For instance, if you take a piece of gold, you cannot chemically break it down into simpler substances; it will always remain gold. 3. **Comparison with Other Options**: - **Option A**: "A substance that can be broken down into simpler substances by chemical means." - This statement describes compounds, not elements. Compounds are substances formed when two or more different types of atoms bond together chemically. For example, water (H₂O) is a compound made of hydrogen and oxygen atoms, and it can be broken down into these elements through chemical reactions (like electrolysis). - **Option C**: "A combination of two or more different types of atoms that are chemically bonded together." - This option also describes compounds rather than elements. Compounds consist of different types of atoms that are chemically bonded, such as sodium chloride (NaCl), which is made of sodium and chlorine atoms. Elements, on the other hand, consist of only one type of atom. - **Option D**: "A material that can exist in multiple states such as solid, liquid, and gas." - While it is true that some elements can exist in different states (for example, oxygen can be found as a gas (O₂), and bromine as a liquid), this statement is too broad and does not specifically define what an element is. Many substances, including compounds, can also exist in multiple states depending on temperature and pressure. ### Summary of Key Points: - An element is a pure substance made of only one type of atom. - Elements cannot be broken down into simpler substances by chemical means. - Compounds consist of two or more different types of atoms and can be broken down chemically. - The ability to exist in multiple states is not a defining characteristic of elements. ### Revision Summary: - An element is a pure substance made of one type of atom. - Elements cannot be chemically broken down into simpler substances. - Compounds are made of different types of atoms and can be broken down. - The state of matter (solid, liquid, gas) is not exclusive to elements.