Which of the following 3d-metal ion will give the lowest enthalpy of hydration () when dissolved in water?

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Canvas Classes · Accepted Answer

Concept: Enthalpy of hydration depends on charge density and CFSE

For M²⁺ ions of the same charge, hydration enthalpy is influenced by:
1. Ionic radius — smaller radius → higher charge density → more exothermic hydration
2. Crystal Field Stabilisation Energy (CFSE) — ions with CFSE gain extra stabilisation

(, half-filled) has zero CFSE in any field (all orbitals singly occupied — no net stabilisation from crystal field splitting).

Other ions (: , : , : ) all have non-zero CFSE, which contrib

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