Explain the classification of monohalogen compounds on the basis of $sp^3$ $(C-X)$ bonds.

(N/A) Monohalogen compounds containing $sp^3$ $(C-X)$ bonds are classified into the following categories:
$(a)$ Alkyl Halides: In these,the halogen atom is bonded to an alkyl group. They are further classified as $1^{\circ}$ (primary),$2^{\circ}$ (secondary),and $3^{\circ}$ (tertiary) depending on the nature of the carbon atom to which the halogen is attached.
$(b)$ Allylic Halides: These are the compounds in which the halogen atom is bonded to an $sp^3$ hybridized carbon atom adjacent to a carbon-carbon double bond (i.e.,an allylic carbon).
$(c)$ Benzylic Halides: These are the compounds in which the halogen atom is bonded to an $sp^3$ hybridized carbon atom attached to an aromatic ring.