Define:
(a) Intermolecular force of attraction
(b) Intermolecular space

Hint: Intermolecular forces and intermolecular spaces are responsible for most of the physical and chemical properties of matter. As we know, matter in the surrounding is made up of many same or different kinds of molecules.

Complete Solution :
Let us study both the points one by one:
(a) Intermolecular force of attraction-
- Intermolecular forces also written as IMF; are the forces arising in between the molecules of a substance. Intermolecular force is the force of attraction between the molecules of matter.
- Atoms like hydrogen, oxygen, nitrogen, etc are formed when a required number of electrons, protons and neutrons combine together.
- When two atoms of hydrogen and one atom of oxygen is combined together, they form a water molecule. Thus, a molecule is formed when many atoms combine together.
- When many molecules combine together, they form a compound. For example, when many molecules of water are combined together, we get liquid water.
Therefore, the matter around us is made up of many molecules packed together. States of matter are also in fact classified on the basis of Intermolecular force of attraction between the molecules.

(b) Intermolecular space-
- The space present in between two molecules or atoms is called intermolecular space. If the intermolecular force in between atoms or molecules is strong then the intermolecular space is less and vice versa.
The molecules of solids are tightly packed because of strong intermolecular forces.
-Solids have the strongest intermolecular force of attraction between its molecules and less intermolecular space.
-Liquids have moderate intermolecular force of attraction between its molecules and moderate intermolecular space.
-Gases have less intermolecular force of attraction between its molecules and more intermolecular space.

Note: Students may get confused in between intermolecular and intramolecular forces of attraction.
Do note that intermolecular forces of attraction are the forces of attraction between the molecules of a compound whereas, intramolecular forces of attraction are the forces of attraction between atoms of a molecule.