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Which of the following statements about periodic trends and properties of elements are INCORRECT? (A) Cr2+(g) has a greater magnetic moment than Co3+(g). (B) The atomic size of the group 13 elements follows the order B < Ga < Al < Tl. (C) Lanthanide contraction is responsible for the ionisation energy of Pb being lower than that of Sn. (D) An element whose successive ionisation energies (in kJ/mol) are 332, 738, 849, 4080, 4958,... belongs to Group 15.

1. A and C only
2. B and C only
3. B, C, and D only
4. A and D only

Correct answer: B and C only

Solution

Statement A: Both Cr2+ and Co3+ are d⁴ in gas phase (high-spin), so they have equal magnetic moments -- A is INCORRECT as a statement claiming Cr2+ has greater moment. Statement B: Due to poor d-electron shielding, Ga is actually smaller than Al, so the correct order is B < Al < Ga < Tl; the given order is INCORRECT. Statement C: Lanthanide contraction affects 5d transition metals, not 6p elements like Pb directly; Pb vs Sn IE difference is due to relativistic effects and inert pair effect, not lanthanide contraction. C is INCORRECT. Statement D: Large jump between IE3 (849) and IE4 (4080) means 3 valence electrons -> Group 13, not Group 15. D is INCORRECT.

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