In the context of the question, the correct answer is:
A. element
Elements are substances that cannot be separated into simpler substances by chemical processes. They are composed of only one type of atom. For example, oxygen (O2) is an element composed of oxygen atoms. No chemical reaction can break down oxygen into simpler substances; it remains oxygen. On the other hand, compounds are made up of different elements chemically bonded together, and they can be broken down into simpler substances through chemical reactions. Solutions and suspensions are mixtures that can be separated by physical means, and colloids are mixtures with particles dispersed throughout but can be separated.
Therefore, an element is the only option that cannot be separated into simpler substances or converted into another substance by chemical processes.
