If a container becomes cold during a reaction, what can it indicate?

Correct answer: The reaction absorbed heat

The governing concept is an endothermic energy change. If the container becomes cooler during a reaction, the reacting system may have absorbed heat from the surroundings, lowering the surroundings’ temperature. Therefore option A is correct. A reaction that releases heat would generally warm its surroundings, while burning and metal deposition are specific processes that cannot be concluded merely from cooling. The word “can” appropriately indicates an inference, not proof of one particular reaction.