Nucleic acids, proteins, carbohydrates, and lipids are the four major types of biomolecules that form all living things. These biomolecules consists of monomers linked together by covalent bonds to form polymers.
Nucleic acids, proteins, carbohydrates and lipids can be classified according to their basic elements, monomer constituents, and functions.
Isotopes are variants of a particular chemical element which differ in neutron number (neutral particle)and all isotopes of a given element have the same number of protons (positive particle) in each atom.So isotope B of the sodium will have 11 protons, 11 electrons but it may have a wide range in its number of neutrons.