Answer is: the combined ionic bond strength of CrCl₂ and intermolecular forces between water molecules.
When chromium chloride (CrCl₂) is dissolved in water, the temperature of the water increases, heat of the solution is endothermic.
Dissociation of chromium chloride in water: CrCl₂(aq) → Cr²⁺(aq) + 2Cl⁻(aq).
Energy (the lattice energy) is required to pull apart the oppositely charged ions in chromium chloride.
The heat of hydration is liberated energy when the separated ions (in this example chromium cations and chlorine anions) attract polar water molecules.
Because the lattice energy is higher than the heat of the hydration (endothermic reaction), we can conclude that bonds between ions are strong (the electrostatic attraction between oppositely charged ions).