Step-by-step explanation:
In nuclear reactors, control rods are used because reactions that occur in a nuclear reactor are highly exothermic in nature.
Therefore, when these control rods are infused in a nuclear reactor then it absorbs the neutrons and helps to control the chain reaction. As a result, the rate of chain reaction gets in control.
Thus, we can conclude that the statement control rods are used to slow down the reaction in the reactor core when the core becomes too hot is a true statement.