Which process is exothermic during solution formation?

When considering the process of solution formation and identifying which steps are exothermic, it's essential to understand the thermodynamics involved in the interactions between solute and solvent molecules. In an exothermic reaction, energy is released into the surroundings.

The correct answer, which involves the formation of intermolecular bonds between the solute and solvent, is exothermic because when these new interactions are established, energy is released. This release occurs as the attractive forces between the solute and solvent molecules overcome the energy required to separate them initially.

In contrast, breaking intermolecular bonds between solute molecules or between solvent molecules requires an input of energy, making those processes endothermic. Mixing solute with solvent is a broad term that encompasses various interactions and may not be specifically indicative of energy changes without further context. This generalization again differs from the precise exothermic nature of bond formation.

Thus, the formation of new intermolecular bonds between the solute and solvent is what contributes to the release of energy, characterizing the process as exothermic.