Final answer:
A compound is a substance that can only be separated into its constituent elements by chemical means, as it consists of chemically bonded atoms in a fixed ratio. Option 4 is correct.
Step-by-step explanation:
The substance that can only be separated by chemical means and cannot be separated physically is a compound. A compound consists of atoms of two or more elements chemically combined in a fixed, whole-number ratio.
Unlike mixtures, which can be separated into their components by physical means, compounds require chemical reactions to break them down into their constituent elements. For example, table salt is a compound made of sodium and chlorine and can only be broken down into these elements through chemical processes.
A compound is a substance that can only be separated by chemical means and cannot be separated physically. This means that option 4) A compound is the correct answer to your question. A compound is a substance composed of two or more elements chemically combined in a fixed ratio. The atoms in a compound are held together by chemical bonds, and breaking these bonds requires a chemical reaction.