Step 1: {Intramolecular Hydrogen Bonding}
In o-nitrophenol, the hydrogen of the \({O-H}\) group and the oxygen of the nitro group form intramolecular hydrogen bonding producing a six-membered ring structure. In m-nitrophenol, p-nitrophenol, and phenol, intermolecular hydrogen bonding is present.
Hence, the correct answer is (A).