The diagram shows the antigen-binding site of an antibody (grey) and the ligand portion of a bound antigen (blue). Select the type of bond made between the highlighted amino acid (red) and the antigen. Then hit ‘check’.
The three weak interactions involved in protein structure and in protein–ligand interaction are described in your text book. In summary:
Ionic bonds (Electrostatic interactions) occur between oppositely charged atoms. In proteins these are typically on acidic and basic side-chains.
Hydrogen bonds occur between a hydrogen atom covalently bound to a relatively electronegative atom — usually oxygen or nitrogen in proteins — and another electronegative atom (again usually oxygen or nitrogen). Common hydrogen-bond donors in proteins are hydroxyl and amide side-chains.
Hydrophobic interactions result from the van der Walls interactions between suitably close hydrophobic atoms. In proteins these are typically aliphatic and aromatic side-chains.