Identify the correct decreasing order of nucleophilicity for the following molecules: (i) H ₂ O (ii) H ₂ S (iii) H ₂ Se

Step-by-step solution

Nucleophilicity depends on the polarizability of the donor atom. Down the group in the periodic table, the atomic size increases, which leads to an increase in the polarizability of the electron cloud. A more polarizable electron cloud can easily distort to donate its electron pair to an electrophile. The order of atomic size of the central atoms is O Therefore, the polarizability and nucleophilicity follow the order H ₂ Se > H ₂ S > H ₂ O . This corresponds to the sequence (iii) > (ii) > (i). Answer: (iii) > (ii)