The part of making a solution that always releases energy is the overall change in forming the solution. The answer is letter D. Although letters A, B and C can be viable answers but, it is not always the case. There are some substances that when you mix or separate them requires more energy or less energy. An example would be when the formation (or enthalpy of formation) of carbon
dioxide is negative, it means that it releases heat to the surroundings. When
it releases heat to the surroundings, the reaction is exothermic. Another example is when you mix baking soda and muriatic acid, the resulting mixture is colder. When it is cold, it means that the reaction is endothermic. So the best answer is letter D.
