Answer: the temperature of the container/flask will decrease.
Justification:
1) As stated in the question, the heat of the solution is endothermic.
Endothermic is a process (physical or chemical) in which energy is absorbed from the surroundings by the initial substances to end in the final state.
2) The fact of absorbing heat energy will translate in the decrease of temperature of the surroundings, in this case the container/flask.
