Dry ice is an everyday example of which physical process, in which a solid changes directly into a gas without passing through the liquid state?

Introduction / Context:
Dry ice is the common name for solid carbon dioxide. It is widely used for cooling, special effects, and preservation because of its interesting physical behavior. When exposed to normal atmospheric conditions, dry ice does not melt into a liquid like ordinary ice. Instead, it seems to vanish, turning directly into gas. This question asks you to identify the name of that physical process from the given options, a concept that belongs to basic physics and chemistry.

Given Data / Assumptions:

- Dry ice is solid carbon dioxide. - In normal conditions, it changes directly from solid to gas. - The options are condensation, evaporation, sublimation, and freezing.

Concept / Approach:
The change of state directly from solid to gas, without passing through the liquid phase, is called sublimation. In contrast, condensation is gas to liquid, evaporation is liquid to gas, and freezing is liquid to solid. Since dry ice goes from solid to gaseous carbon dioxide under normal temperatures and pressures, the only correct process name is sublimation. Recognising definitions of the basic phase changes is the key to solving this question.

Step-by-Step Solution:
Step 1: Recall the definition of sublimation as the direct conversion of solid to gas without forming a liquid. Step 2: Think about what you observe when dry ice is left in the open. It does not form a pool of liquid carbon dioxide but instead produces fog like vapour as it turns into gas. Step 3: Match this behavior with the definition of sublimation. Step 4: Check the other options: condensation (gas to liquid), evaporation (liquid to gas), and freezing (liquid to solid) do not match the description. Step 5: Conclude that the correct answer is sublimation.

Verification / Alternative check:
Any basic science textbook or reliable educational resource on states of matter will list dry ice as the classic example of sublimation. They show diagrams of carbon dioxide phase changes and explain how at atmospheric pressure, solid carbon dioxide sublimes directly into gaseous carbon dioxide without forming a liquid state.

Why Other Options Are Wrong:
- Condensation: This is when gas changes to liquid, such as water vapour turning into droplets on a cold surface. - Evaporation: This is the change from liquid to gas, for example water turning into water vapour. - Freezing: This is the change from liquid to solid, like water freezing into ice.

Common Pitfalls:
Students sometimes confuse sublimation with evaporation or assume that any gas formation is evaporation. The important difference is the starting state: sublimation begins from a solid, while evaporation begins from a liquid. Keeping a clear mental table of phase changes helps avoid wrong answers in similar questions about physical processes.

Final Answer:
Dry ice is an everyday example of sublimation, the direct change of state from solid to gas without becoming liquid.