The correct option is **B. An element is a pure substance that cannot be broken down into simpler substances by chemical means.** ### Detailed Explanation: 1. **Definition of an Element**: - An element is defined as a fundamental substance that cannot be broken down into simpler substances through chemical reactions. Each element is made up of only one type of atom, which is characterized by its atomic number (the number of protons in its nucleus). For example, hydrogen (H) is an element consisting solely of hydrogen atoms. 2. **Why Option B is Correct**: - Option B accurately captures the essence of what an element is in chemistry. It emphasizes that elements are pure substances, meaning they consist of only one type of particle (atoms) and cannot be decomposed into simpler substances by any chemical process. This is a fundamental concept in chemistry, as elements serve as the building blocks for all matter. 3. **Why the Other Options are Incorrect**: - **Option A: An element is a substance made up of two or more different types of atoms.** - This statement is incorrect because it describes a compound, not an element. A compound is 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. An element, on the other hand, consists of only one type of atom. - **Option C: An element is a combination of atoms that are chemically bonded together.** - This option is misleading because it suggests that an element is made up of multiple atoms bonded together. While it is true that elements can exist as diatomic molecules (like O₂ or N₂), they still consist of only one type of atom. Therefore, this definition is more applicable to compounds rather than elements. - **Option D: An element is a solution that contains dissolved ions in water.** - This statement is incorrect because it describes a solution, which is a homogeneous mixture of two or more substances. An element is not a mixture or a solution; it is a pure substance. Solutions can contain ions, but they do not represent the definition of an element. ### 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 bonded together. - Solutions are mixtures and do not define what an element is. ### Revision Summary: - Elements are pure substances that cannot be chemically broken down. - Each element consists of only one type of atom. - Compounds are formed from two or more different types of atoms. - Solutions are mixtures and do not represent elements.