Hello!
The intermolecular force that exists between a calcium ion and water is the ion-dipole force.
The Calcium ion (Ca⁺²) represents the "ion" in the ion-dipole force, while water represents the "dipole". The chemical structure of water (H₂O) is an angled one, where there is a permanent dipole towards the Oxygen atom, making it become slightly negative. The positive Calcium ion attracts the slightly negative oxygen atom in water by electrostatic forces and an ion-dipole interaction is formed.
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