Assertion (A): Linkage isomerism arises in coordination compounds because of ambidentate ligand.
Reason (R): Ambidentate ligand like NO₂ has two different donor atoms i.e., N and O.

Linkage isomerism is the existence of coordination compounds that have the same chemical formula but differ in the connectivity of the ligand to the metal.

Linkage isomerism arises in coordination compounds containing ambidentate ligands because ambidentate ligands have two different donor atoms.
Ambidentate ligand is a type of ligand that tends to bind the central atom via two different donor atoms, which lead to the formation of linkage isomers.

Examples: NO₂ ion can bind to the central metal atom or ion with either nitrogen or oxygen atom.

So, the reason is also a correct statement.

Hence, both the assertion and the reason are correct statements, and reason is the correct explanation for the assertion.