Answer: Option (c) is the correct answer.
When an atom donates or shares its valence electrons with other atoms then it results in the formation of a new atom. This means a chemical has occurred as the chemical composition of products will be different from the reactants.
Whereas a substance is a matter which contains specific composition with some specific properties.
When two or more substance are mixed together then it is known as a mixture. It is not necessary that substances added will combine with each other.
When atoms of similar element chemically combine together then they result in the formation of a molecule.
For example,
Therefore, we can conclude that when components do not combine chemically, it is a mixture.