Which of the following sentences describes an example of sublimation?

• A. Water boils and changes from liquid to vapor.
• B. Iron rusts when exposed to oxygen and moisture.
• C. Solid dry ice (CO_2) turns directly into carbon dioxide gas without forming a liquid.
• D. Ice melts into liquid water when left at room temperature.

Answer: (C)

Verified step by step guidance

1. Understand the definition of sublimation: it is the process where a substance changes directly from a solid to a gas phase without passing through the liquid phase.
2. Analyze each sentence to identify the phase changes involved:
3. 1. 'Water boils and changes from liquid to vapor' describes a liquid-to-gas transition (evaporation or boiling), not sublimation.
4. 2. 'Iron rusts when exposed to oxygen and moisture' is a chemical reaction (oxidation), not a phase change.
5. 3. 'Solid dry ice (CO_2) turns directly into carbon dioxide gas without forming a liquid' matches the definition of sublimation because it goes from solid directly to gas.
6. 4. 'Ice melts into liquid water when left at room temperature' is a solid-to-liquid phase change (melting), not sublimation.