When we make a mixture, the molecules and bonds present in each of the substances can exert attraction or repulsion and can absorb or release energy. This energy is evidenced by an increase or decrease in temperature.
When the mixture releases energy, the temperature will increase and is called exothermic. When the mixture absorbs energy, the temperature will decrease and is called endothermic.
Therefore, if the beaker becomes cold it means that the mixture of these two compounds is endothermic.
Answer: D.) Dissolving this solute is an endothermic process.