The correct option is **D. endothermic**. ### Explanation of the Correct Answer 1. **Definition of Endothermic Reactions**: - An endothermic reaction is a type of chemical reaction that absorbs heat from its surroundings. This means that during the reaction, energy in the form of heat is taken in, leading to a decrease in the temperature of the surroundings. 2. **Energy Changes in Reactions**: - In chemical reactions, energy changes are crucial. Reactions can either release energy (exothermic) or absorb energy (endothermic). The energy absorbed in an endothermic reaction is often used to break bonds in the reactants, allowing the reaction to proceed. 3. **Examples of Endothermic Reactions**: - A common example of an endothermic reaction is the process of photosynthesis in plants, where carbon dioxide and water absorb sunlight (heat) to produce glucose and oxygen. - Another example is the dissolution of ammonium nitrate in water, which feels cold to the touch because it absorbs heat from the surroundings. ### Why the Other Options are Incorrect - **A. Thermodynamic**: - This term refers to the study of energy transformations and the laws governing these transformations. While thermodynamics encompasses both endothermic and exothermic reactions, it does not specifically refer to reactions that absorb heat. Therefore, this option is too broad and not specific to the question. - **B. Exothermic**: - An exothermic reaction is the opposite of an endothermic reaction. It releases heat into the surroundings, resulting in an increase in temperature. Since the question specifically asks about reactions that absorb heat, this option is incorrect. - **C. Isothermal**: - An isothermal process is one that occurs at a constant temperature. While it can involve heat transfer, it does not specifically indicate whether heat is absorbed or released. Therefore, this term does not accurately describe a reaction that absorbs heat. ### Summary of Key Points - **Endothermic reactions absorb heat**, leading to a decrease in the temperature of the surroundings. - **Exothermic reactions release heat**, which is the opposite of endothermic reactions. - **Thermodynamics** is a broader field that includes both types of reactions but does not specifically refer to heat absorption. - **Isothermal processes** maintain constant temperature but do not specify the direction of heat transfer. ### Revision Summary - Endothermic reactions absorb heat from the surroundings. - Exothermic reactions release heat, increasing the temperature of the surroundings. - Thermodynamics is the study of energy changes, not specific to heat absorption. - Isothermal processes occur at constant temperature, not necessarily involving heat absorption.