Answer : Chemicals A and B form an endothermic reaction, and chemicals C and D form an exothermic reaction.
Explanation :
Endothermic reaction : When the system absorb heat from the surrounding then the surrounding become cool.
Exothermic reaction : when the system releases heat into the surrounding then the surrounding become hot.
According to the question,
when we mixed chemical A and chemical B together in a test tube to form chemical C, the mixture become cool. This means that the system is absorbing heat from the surrounding and thus the reaction is called a endothermic reaction.
And when we added chemical D in chemical C, the new mixture becomes hot and explodes. This means that the system is releasing heat into the surrounding and thus the reaction is called as exothermic reaction.
