What is the correct increasing order of nucleophilicity?

Cl^– < Br^– < I^-

The correct increasing order of nucleophilicity is (1) \(Cl^– < Br^– < I^–\).

Nucleophilicity is the tendency of an atom or molecule to donate a pair of electrons to form a chemical bond. The larger the electron cloud around an atom, the more nucleophilic it is. In the halogens, the electron cloud gets larger as you go down the periodic table, so the nucleophilicity increases in the order \(Cl^– < Br^– < I^–\).