A sample of a compound is added to distilled water in a clean beaker. A reaction occurs and the water temperature drops rapidly which indicates that an endothermic reaction occurred. Hence, option A is correct.
Endothermic reactions are chemical reactions in which the reactants absorb heat energy from the surroundings to form products.
An endothermic reaction means that heat is absorbed during this reaction (enthalpy change value has a positive sign).
During the endothermic reaction heat is absorbed from the surroundings (here, water) and hence the temperature of the water in which the reaction is taking place decreases.
Hence, option A is correct.
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