Which reactant in each of the following pairs is more nucleophilic? Explain.

a) BF₃ or F^-

The nucleophiles are the negatively charged ions or neutral species that have a lone pair of electrons and are ready for bonding.

1. Nucleophile attacking the same atom then nucleophilicity is same as basicity that more basic species is more nucleophilic in nature.
2. Nucleophilicity increases in going down in a group of the periodic table.
3. A negatively charged nucleophile is more nucleophilic than a neutral nucleophile due to a negative charge.

On the basis of:

Rule3: A negatively charged nucleophile is more nucleophilic than a neutral nucleophile due to a negative charge.

BF₃is not a nucleophile even B(Boron) have empty d orbitals to gain electrons rather than to give electrons which nucleophile do.

F^-is more nucleophilic thanBF₃