Final answer:
Halide ion nucleophilicity in methanol solution decreases with increasing electronegativity, so the correct order is I- > Br- > Cl- > F-. Iodide is the most nucleophilic and fluoride is the least.
Step-by-step explanation:
To rank the relative nucleophilicity of halide ions in a methanol solution, one must consider several factors, such as the bond length, electronegativity, and the ability of halides to serve as leaving groups. Nucleophilicity is often closely related to the basicity of the ion; thus, halide ions with lower electronegativity tend to be more nucleophilic.
Based on this understanding, the tendency of halides to act as nucleophiles decreases with increasing electronegativity: I- (least electronegative, more nucleophilic) > Br- > Cl- > F- (most electronegative, least nucleophilic).
Therefore, the nucleophilicity order is I- > Br- > Cl- > F- in methanol solution.