Which of the following physical processes of a pure substance releases energy (heat) to the surroundings?

Introduction / Context:
This physics question examines your understanding of energy changes during phase transitions of a pure substance. When a substance changes state—for example from liquid to gas or gas to liquid—heat is either absorbed from or released to the surroundings. The question asks which listed process releases energy, meaning it is exothermic. Recognising which changes are exothermic versus endothermic is important in meteorology, engineering, and daily life phenomena such as sweating or cloud formation.

Given Data / Assumptions:

• The focus is on physical processes of a pure substance, specifically changes of state and whether they release or absorb heat.
• Options include condensation, fermentation, evaporation, and none of the above.
• We interpret fermentation here as a biochemical process, not a simple physical phase change; the emphasis is on physical changes like evaporation and condensation.

Concept / Approach:
For a pure substance, phase changes that require energy input (endothermic) include melting (solid to liquid), evaporation or boiling (liquid to gas), and sublimation (solid to gas). In these processes, the substance absorbs heat from the surroundings. Phase changes that release energy (exothermic) include condensation (gas to liquid), freezing (liquid to solid), and deposition (gas to solid). During condensation, gas molecules lose kinetic energy as they come together to form a liquid; the energy they lose is released as heat to the surroundings. Evaporation is the reverse: high energy molecules escape from the liquid, and the liquid absorbs heat from the surroundings to replenish this energy, which is why evaporation causes cooling. Fermentation is a biochemical reaction rather than a simple physical phase change and is not the focus of basic phase change discussions in this type of question.

Step-by-Step Solution:

Verification / Alternative check:
Thermodynamics and school physics texts list the latent heat of vaporisation (for evaporation/boiling) as heat absorbed by the liquid and the latent heat of condensation as heat released when vapour condenses. Meteorology examples explain that when water vapour condenses in the atmosphere to form clouds, latent heat is released and can drive air movements. Everyday experience also supports this; steam condensing on skin can feel very hot because it releases heat quickly. These examples confirm that condensation is an exothermic process, while evaporation is endothermic, making condensation the correct answer in this context.

Why Other Options Are Wrong:

Fermentation, a biochemical process converting sugars to alcohol, is wrong in this context because it is a chemical, not a simple physical phase change; the question focuses on processes like condensation and evaporation.

Evaporation, when a liquid changes to vapour at the surface, is incorrect because evaporation absorbs heat from the surroundings and causes cooling rather than releasing heat.

None of the above processes release energy is wrong because condensation clearly releases heat to the surroundings as vapour turns into liquid.

Common Pitfalls:
Students sometimes mix up condensation and evaporation because they are reverse processes and may assume both behave similarly with respect to heat. Another pitfall is to pay attention only to temperature changes and ignore whether the substance or the surroundings gain or lose heat. To avoid these errors, remember that condensation (gas to liquid) releases heat to the surroundings, whereas evaporation (liquid to gas) requires heat input and cools the surroundings.