Hello!
As a chemical reaction occurs and the thermometer in the container records a decrease in temperature, the statement that is true about the reaction is: The reaction is endothermic because heat was taken in by the reaction.
Endothermic reactions are those that require energy in the form of heat to be completed. Technically, in these reactions, the enthalpy of the products is higher than the enthalpy of the products. The requirement of energy causes the temperature to decrease. A general expression for an endothermic reaction can be written in the following way:
A + Δ → B (Where Δ means heat)
Have a nice day!