Fajan's rule states that small, highly charged ions tend to form more:

Explanation

Fajan's rule explains that small, highly charged ions have high polarizing power due to their charge density. This leads to greater distortion of the electron cloud of the anion, increasing the covalent character of the bond. Hence, they tend to form covalent compounds. Option A, ionic compounds, is incorrect because such ions form bonds with significant covalent character rather than purely ionic bonds. Option B, polymeric compounds, is unrelated to Fajan's rule, which focuses on the nature of individual ionic bonds, not polymerization. Option D, coordination compounds, involves complex formation and ligand interactions, which are not directly addressed by Fajan's rule.