Final answer:
A cake baking is an example of an endergonic reaction that absorbs energy, while a candle burning, a firework exploding, and wood smoldering are exothermic reactions that release energy.
Step-by-step explanation:
The question at hand requires us to identify which of the given options is an example of a reaction that absorbs energy. Out of the listed activities A. a cake baking, B. a candle burning, C. a firework exploding, and D. a piece of wood smoldering, the one that absorbs energy is A. a cake baking. This is because the process of baking a cake involves endergonic reactions, where energy, typically in the form of heat from the oven, is absorbed to facilitate the chemical changes in the cake's batter. On the contrary, a candle burning, a firework exploding, and wood smoldering are all examples of exothermic reactions, wherein they release energy in the form of heat or light.