Answer:
B
Step-by-step explanation:
In an exothermic process the enthalpy of the products is smaller than the enthalpy of the reactives, in other words, the difference of enthalpy of the process (which is defined as the enthalpy at the final state of the process minus the enthalpy of the initial state) is negative. In this case, this means that the enthalpy of solid barium hydroxide plus pure water is greater than that of the solution, at the same temperature .