Answer: It is a giant lattice of oppositely charged ions.
Explanation:
Ionic compound is formed by the transfer of electrons. For formation of a neutral ionic compound, the cation is formed by loss of electrons by metals and anions are formed by gain of electrons by non metals. The cations and anions being oppositely charged attract each other through strong coloumbic forces and form an ionic bond.
The cations and anions are arranged in a unit cell and there are many unit cells arranged together to form a regular lattice. Thus they are hard and crystalline in nature.