Answer: molecule
Explanation:
Covalent bond is the type of bond formed when there is sharing of electrons between two similar or different atoms.
1. Proton is the subatomic particle of an atom which is present in the nucleus of atom and bears positive charge.
2. Ions are formed when there is a loss or gain of electrons in an atom.
3. An atom is smallest unit of a matter or substance.It consist of three subatomic particles : electrons, protons, neutrons.
4. Molecules of element is a pure substance which is formed by bonding of atoms of similar elements. Example: [tex]H_2[/tex] .Molecule of compound is a pure substance which is formed by bonding of atoms of different elements combined together in a fixed ratio by mass. Example: [tex]H_2O[/tex]
