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Which of the following are CORRECT orders?

1. KCl > KBr (lattice energy)
2. AlN > MgO (lattice energy)
3. Li+(aq) > Cs+(aq) (ionic mobility in solution)
4. Li+(aq) < Cs+(aq) (electrical conductivity in solution)

Correct answer: KCl > KBr (lattice energy)

Solution

A: KCl vs KBr — same K+ cation; Cl- has smaller radius than Br-, so interionic distance is shorter → higher lattice energy for KCl. CORRECT. B: AlN (Al3+/N3-, charge product = 9) vs MgO (Mg2+/O2-, charge product = 4) — higher ionic charges lead to much higher lattice energy for AlN. CORRECT. C: Ionic mobility in solution depends on hydrated ion size. Li+ is small and highly hydrated → large hydrated radius → lower mobility than Cs+. So Li+(aq) < Cs+(aq) in mobility. INCORRECT as stated. D: Electrical conductivity in solution depends on mobility. Since Li+(aq) has lower mobility, Li+ contributes less conductivity → Li+ < Cs+ in conductivity. CORRECT. Correct options: A, B, D.

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