Answer:
С. a single component that can't be separated
Explanation:
Substance : It is the pure form of matter or we can say that it is a matter that contains only one type of molecule of atom. It can not be separated by physical process.
For example : Water is a substance.
Mixture : It is a combination of different type of atoms or molecules and it is an impure form.
For example : Sodium chloride with water is a mixture.
Hence, the correct option is, (C) a single component that can’t be separated.