Question

Which of the following processes describes the direct transition of a substance from a solid state to a gaseous state without passing through the liquid state?

• A. Evaporation
• B. Condensation
• C. Sublimation
• D. Deposition

Hint:

Remember the shortcut: \[ \text{Solid} \rightarrow \text{Gas} = \text{Sublimation} \] \[ \text{Gas} \rightarrow \text{Solid} = \text{Deposition} \] Examples of sublimation: Camphor, Iodine, Naphthalene, Dry Ice.

Answer 1

The Correct Option is C

Concept: Matter exists primarily in three physical states—solid, liquid, and gas. When energy is supplied or removed, substances undergo phase transitions. One such special phase change is sublimation, in which a solid directly changes into a gas without becoming a liquid.

Step 1: Understanding Sublimation.
Sublimation is the process in which a substance changes directly from the solid state to the gaseous state without passing through the liquid state. \[ \text{Solid} \rightarrow \text{Gas} \] During this process, particles absorb sufficient energy to overcome intermolecular forces and escape directly into the gaseous phase.

Step 2: Examples of Sublimation. Common substances that undergo sublimation include:

• Camphor

• Naphthalene balls

• Iodine crystals

• Dry Ice (solid carbon dioxide)

• Ammonium chloride
For example, naphthalene balls gradually disappear when left in open air because the solid directly converts into vapor.

Step 3: Why Option (C) is Correct. Sublimation specifically refers to the direct conversion: \[ \text{Solid} \rightarrow \text{Gas} \] without an intermediate liquid phase. Therefore, Sublimation is the correct answer.

Step 4: Analysis of Other Options.

• Evaporation: Evaporation is the conversion of a liquid into vapor from its surface. \[ \text{Liquid} \rightarrow \text{Gas} \] Hence, it is not the required process.

• Condensation: Condensation is the reverse of evaporation. \[ \text{Gas} \rightarrow \text{Liquid} \] Examples include cloud formation and dew.

• Deposition: Deposition is the reverse of sublimation. \[ \text{Gas} \rightarrow \text{Solid} \] Examples include frost formation on cold surfaces.

Step 5: Relationship Between Sublimation and Deposition. \[ \text{Solid} \xrightarrow{\text{Sublimation}} \text{Gas} \] \[ \text{Gas} \xrightarrow{\text{Deposition}} \text{Solid} \] These are opposite processes and occur without passing through the liquid state. Thus, the direct transition from solid to gas is called

Sublimation.