Which of these describes an endothermic process?

The options is as follows:

a. When lithium is placed in water, the temperature of the container increases.

b. The combustion of kerosene releases heat.

c.  When barium hydroxide is mixed with ammonium chloride, ice crystals form on the outside of the container.

d. The reaction of trinitrotoluene with oxygen releases heat and light.

c.  When barium hydroxide is mixed with ammonium chloride, ice crystals form on the outside of the container.

Explanation:

An endothermic reaction is a chemical reaction whereby heat or energy is absorb from the environment. The heat absorb from the environment is used to provide the activation energy needed for the reaction to be carried out. This energy can be absorbed in the form of heat, light and electricity.

In endothermic reaction their is an overall decrease in the temperature as heat is usually absorb from the surrounding . Usually, after the reaction the components feel cold. Examples of endothermic reaction is dissolving salt in water. Other example of endothermic process are cooking an egg and evaporating liquid water.

Note not all endothermic process are chemical reaction because chemical reaction usually involve breaking or formation of chemical bond. Example of endothermic process that are not chemical  reaction is sweating.

All the other process, their is a release of heat to the surrounding except When barium hydroxide is mixed with ammonium chloride, ice crystals form on the outside of the container.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)