In methanol (protic solvent), nucleophilicity is determined by basicity and solvation effects. Smaller ions are heavily solvated by the protic solvent, reducing their effective nucleophilicity.
C₂H₅O⁻ (ethoxide) is the strongest nucleophile as it is less solvated and highly basic.
C₆H₅O⁻ (phenoxide) is weaker due to resonance stabilization by the benzene ring.
F⁻ is highly solvated despite high basicity, reducing its nucleophilicity significantly.
I⁻ is the best nucleophile because it is the largest ion and least solvated in methanol.
The correct order is I⁻ > C₂H₅O⁻ > C₆H₅O⁻ > F⁻.