In moving down a group, the basicity and nucleophilicity are inversely related, i.e. nucleophilicity increases while basicity decreases. In going from left toright across a period, the basicity and nucleophilicity are directly related. Both of the characteristicsdecrease as the electronegativity of the atom bearing lone pair of electrons increases. If the nucleophilic centre of two or more species is same, nucleophilicity parallels basicity, i.e. more basic the species, stronger is its nucleophilicity. Hencebased on the above facts, the correct order of nucleophilicity will be