Answer: A substance is a single component that can't be separated by the physical process therefore the correct answer is option C.
Explanation: A chemical compound is a mixture of two or more chemical components, whether they are related or unrelated.
For instance, the molecular H2O is composed of one hydrogen atom and two oxygen atoms.
For instance, water is a material that cannot be physically divided yet may be separated using electrolysis.
Mixture: This impure form is made up of several different kinds of atoms or molecules.
A mixture is, for instance, sodium chloride and water.
As a result, (C), a single, irreducible component, is the right answer.