Which of the following phase changes is an example of an exothermic process where a substance releases heat to its surroundings?

Introduction / Context:
Phase changes involve energy exchange between a substance and its surroundings. Some processes absorb heat (endothermic), while others release heat (exothermic). Understanding which changes are exothermic is important in chemistry, meteorology, and everyday situations like freezing water or condensation on a cold glass. This question asks you to identify which listed phase changes are exothermic.

Given Data / Assumptions:

• We consider phase changes at constant pressure.
• The listed changes include liquid to solid, gas to solid, and gas to liquid.
• We are asked which involve release of heat to the surroundings.

Concept / Approach:
When a substance moves from a higher energy phase to a lower energy phase, it releases latent heat and the process is exothermic. Gas has more energy than liquid, and liquid has more energy than solid for the same substance at a given temperature. Therefore, gas to liquid and liquid to solid are exothermic. Gas to solid is also exothermic because it skips the intermediate liquid stage but still moves from high energy gas to low energy solid. All three changes listed move to a lower energy phase and thus release heat.

Step-by-Step Solution:
Step 1: Liquid to solid (freezing): When water freezes into ice, it releases latent heat to the surroundings, so freezing is exothermic. Step 2: Gas to liquid (condensation): When water vapour condenses into liquid water, it releases latent heat, warming the surrounding air; thus condensation is exothermic. Step 3: Gas to solid (deposition): Examples include frost formation when water vapour converts directly to ice on cold surfaces. This also releases heat to the surroundings. Step 4: Since all individual processes listed are exothermic, the correct combined choice is that all of them are examples of exothermic changes.

Verification / Alternative check:
You can remember that melting, evaporation, and sublimation (solid to gas) are endothermic, as they require adding heat to move to a higher energy phase. The reverse processes, such as freezing, condensation, and deposition, are exothermic because the substance gives up energy. Weather forecasts often mention latent heat release during condensation and cloud formation, confirming that these phase changes warm the surroundings.

Why Other Options Are Wrong:
Liquid to solid (freezing) only: While this is exothermic, it is not the only exothermic process listed. Gas to solid (deposition) only: This is also exothermic but does not include the other correct options. Gas to liquid (condensation) only: Condensation is exothermic, but again, the other listed processes share this property.

Common Pitfalls:
A common confusion is to assume that gas to solid must be endothermic because it sounds like two steps combined. In reality, deposition is just the reverse of sublimation and is exothermic. Another pitfall is to memorise only one or two examples without understanding the general rule that moving to a more ordered, lower energy phase releases heat.

Final Answer:
All the listed phase changes involve release of heat to the surroundings, so the correct choice is All of the above.