Answer:
C. Exothermic Reaction
Explanation:
Let's go through the choices
A. Combustion - Combustion is a highly exothermic / redox reaction which produces light and heat (i.e basically it bursts into flames). In the description, the only reaction is that it feels warm, hence this is not the answer.
B. Endothermic - Recall that endothermic reactions absorbs heat and thus cools the surroundings thereby making test tube feel cooler. this is obviously not the case so this is not the answer.
C. Exothermic - Recall that exothermic reactions releases heat and thus causes the surroundings thereby making the test tube feel warmer (or hotter in some cases). This describes our situation so THIS IS THE ANSWER.
D. Endergonic reactions require an input of energy from an external source that is adsorbed by the reaction (for example if heat was applied by an external source). In this case, there is no mention of additional energy sources. Hence this is probably not the answer.
