Give the classification of crystalline solids.

(N/A) Crystalline solids are classified based on the nature of the intermolecular forces or bonds that hold the constituent particles together.
These are classified into four main categories:
$(i)$ Ionic solids: Held together by strong electrostatic forces of attraction between ions (e.g.,$NaCl$,$ZnS$).
$(ii)$ Covalent (Network) solids: Held together by covalent bonds forming a continuous network (e.g.,$SiO_2$,diamond,graphite).
$(iii)$ Metallic solids: Held together by metallic bonds involving a sea of delocalized electrons (e.g.,$Fe$,$Cu$,$Ag$).
$(iv)$ Molecular solids: Held together by Van der Waals forces or hydrogen bonds (e.g.,$I_2$,$P_4$,$H_2O$).
In graphite,the presence of free electrons makes it a good conductor of electricity.