which molecule or ion needs only two resonance structures to describe its bonding
Resonance (chemistry) The ozone molecule is represented by two resonance structures. In reality the two terminal oxygen atoms are equivalent and the hybrid structure is drawn on the right with a charge of − 1⁄2 on both oxygen atoms and partial double bonds with a full and dashed line and bond order  1 1⁄2.[15][16]
Antigen-antibody interaction Antibodies bind antigens through weak chemical interactions, and bonding is essentially non-covalent. Electrostatic interactions, hydrogen bonds, van der Waals forces, and hydrophobic interactions are all known to be involved depending on the interaction sites.[6][7]