In thermochemistry, an endothermic reaction is best described as which of the following types of process?

Introduction / Context:
This question belongs to basic thermochemistry and energetics. Reactions can be classified as exothermic or endothermic depending on whether they release or absorb heat. Recognising the correct definition of an endothermic reaction is essential for understanding energy changes in chemical processes such as dissolving, melting and decomposition reactions.

Given Data / Assumptions:

• The term being defined is endothermic reaction.
• Options describe reactions that either release heat, absorb heat, or do neither.
• We assume standard chemistry definitions where the system is the reacting substances and surroundings is everything else.

Concept / Approach:
An endothermic reaction is one in which the reacting system absorbs heat energy from its surroundings. As a result, the surroundings may feel cooler. Typical examples include melting of ice and thermal decomposition reactions. In contrast, exothermic reactions release heat to the surroundings and often cause a temperature increase. Therefore, the correct description of an endothermic reaction must include absorption of heat from the surroundings.

Step-by-Step Solution:

Verification / Alternative check:
Consider familiar examples. When ammonium nitrate dissolves in water in an instant cold pack, the pack becomes cold because the dissolution is endothermic and absorbs heat from the surroundings. Similarly, the melting of ice requires heat input, so it is endothermic. In these cases, a thermometer placed in the surroundings registers a temperature drop. These observations are consistent with the definition that endothermic reactions absorb heat from the surroundings, confirming option B as correct.

Why Other Options Are Wrong:

• A reaction in which heat is released to the surroundings: This describes an exothermic reaction, not an endothermic one.
• A reaction in which neither heat is released nor absorbed: In practical terms most reactions involve some heat effect, and this is not the standard definition of endothermic.
• A reaction in which heat and work both remain unchanged: This does not relate to the specific concept of endothermic or exothermic processes.
• A reaction that only produces light but no heat at all: Many light producing reactions still involve heat changes, and this description is not a definition of endothermic behaviour.

Common Pitfalls:
Students often confuse exothermic and endothermic because both involve energy changes and may think of fire or heat in general terms rather than direction of heat flow. Focusing on the prefixes exo meaning out and endo meaning in helps. Another useful strategy is to draw an energy diagram and note whether the products are at a higher or lower energy level than the reactants. For endothermic reactions, products are at higher energy and the system must absorb heat from the surroundings to climb that energy difference.

Final Answer:
An endothermic reaction is A reaction in which heat is absorbed from the surroundings.