Reactivity of Nucleophiles:

Nucleophiles are the species which have a tendency to donate an electron pair to an electrophile. The reactivity of nucleophiles depends on various factors such as:

1. Basicity: Nucleophilicity increases with increasing basicity as basicity increases the affinity of nucleophile to donate an electron pair increases.

2. Solvent: The polarity of the solvent affects the nucleophilicity as polar solvents stabilize the nucleophile whereas non-polar solvents destabilize the nucleophile.

3. Steric Hindrance: Bulky groups present on the nucleophile decreases its nucleophilicity as it becomes difficult for the nucleophile to approach the electrophilic centre.

4. Charge: Negatively charged nucleophiles are more reactive than neutral nucleophiles.

5. Electronegativity: The higher the electronegativity of the atom bearing the nucleophile, the less reactive the nucleophile.

Answer:

Among the given options, the most reactive nucleophile is CH3O- which is methoxide ion. The reason is as follows:

1. Basicity: Methoxide ion has high basicity due to the presence of a negative charge on oxygen. Therefore, its nucleophilicity is expected to be high.

2. Solvent: Methoxide ion is a polar species and hence polar solvents such as water, methanol, etc. stabilize it. This increases its nucleophilicity.

3. Steric Hindrance: Methoxide ion is a small-sized ion and hence does not have any significant steric hindrance. Hence, its nucleophilicity is not affected.

4. Charge: Methoxide ion is negatively charged and hence more reactive than neutral nucleophiles.

5. Electronegativity: Oxygen is highly electronegative and hence decreases the nucleophilicity of methoxide ion.

Therefore, based on the above factors, CH3O- is the most reactive nucleophile among the given options.