Final answer:
Chloride ion (Cl⁻) has a tendency to form weaker ion pairs with carboxylate groups on proteins due to its nature as a good-leaving group and weaker electrostatic interactions.
Step-by-step explanation:
The question relates to the ion pairing tendencies of various anions with carboxylate groups on protein surfaces. Among the listed ions, Chloride ion (Cl⁻) would have the weakest tendency to form an ion pair with carboxylate groups, not the strongest. This is because chloride ions have high nucleophilicity but are also the best-leaving groups, implying they form weaker electrostatic interactions with other negatively charged groups like carboxylates.
Carboxylate groups are on proteins as a result of the ionization of carboxylic acids, which release a hydrogen ion leaving behind a negatively charged carboxylate ion. Ions that could potentially form stronger ion pairs with carboxylates would be multivalent cations that can form stronger ionic bonds due to their higher charge and ability to bridge between multiple carboxylate groups, which are not represented in the options provided.