The sublimation of solid to gas involves

1. Analyze the question Sublimation is the direct change of a solid into a gas, skipping the liquid state. The question asks what this process involves.

2. Explain the concept

• Changing from solid to gas means the particles move from a tightly packed, ordered arrangement to widely separated, free-moving ones.
• To break the forces holding the particles together, they must take in energy (usually heat) from the surroundings.
• This makes sublimation an endothermic process. Examples are dry ice (solid CO₂), iodine crystals, naphthalene balls (mothballs), and ammonium chloride.

3. Check each option

• A. Energy absorption: Correct. Particles absorb energy to overcome the intermolecular forces, so the process is endothermic.
• B. Vapourization: This is the change from liquid to gas. Sublimation skips the liquid state, so it is not strictly vapourization. (Some textbooks loosely say sublimation combines melting and vapourization, but the standard definition says it does not pass through the liquid state.)
• C. Melting: This is solid to liquid, which does not happen in sublimation.
• D. Osmotic diffusion: Osmosis involves a solvent moving across a semi-permeable membrane, which has nothing to do with sublimation.

4. Answer The correct option is A, energy absorption.

5. Exam tip Remember the direction of energy flow:

• Solid → liquid → gas (melting, vapourization, sublimation) all absorb energy (endothermic).
• Gas → liquid → solid (condensation, freezing, deposition) all release energy (exothermic).

Whenever particles become more free, energy goes in.