Which of these describes an endothermic process? when lithium is placed in water, the temperature of the container increases. the combustion of kerosene releases heat. when barium hydroxide is mixed with ammonium chloride, ice crystals form on the outside of the container. the reaction of trinitrotoluene with oxygen releases heat and light.

The third one down: "When barium hydroxide is mixed with ammonium chloride, ice crystals form on the outside of the container."

This is because an endothermic reaction [process] takes in more energy than it releases. Therefore because a decrease in energy leads to a decrease in temperature, the ice crystals forming show that it must be a endothermic reaction [process].

Hope this helps! :)
AJ