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Per Fajans' rules, which cation is the most polarising for cations of the same size and charge?
AOne with vacant s shell
BOne with noble-gas configuration (ns² np⁶)
COne with pseudo noble-gas configuration ((n−1)d¹⁰ ns⁰)
DOne with half-filled d shell
Answer & Solution
Correct answer: C. One with pseudo noble-gas configuration ((n−1)d¹⁰ ns⁰)
Fajans noted that a cation with **(n−1)d¹⁰ ns⁰** (pseudo noble-gas, typical of post-transition metals) is **more polarising** than one with a true ns² np⁶ configuration, due to poor shielding by the filled d-shell.
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