Answer: 2. Elements
Explanation:
A mineral is a naturally occurring solid which has a definite chemical structure with some unique physical properties.The building blocks of minerals are elements.
1. Rocks are composed of two or more minerals. Thus minerals are the building blocks of rocks.
2. Element is a pure substance which is composed of atoms of similar elements.
3. Isotopes are the atoms of the same elements which have same atomic number but different mass number.
4. Electrons are the subatomic particles of the atom which bear negative charge and revolve around the nucleus.
