Physical Change: Sublimation

- Physical change refers to a change in the physical properties of a substance without altering its chemical composition. It involves a transformation in the state, shape, or size of matter.
- Sublimation is a specific type of physical change where a solid directly changes into a gas without passing through the liquid state.
- When a substance undergoes sublimation, it absorbs energy from the surroundings, causing the particles to gain enough energy to break their intermolecular bonds and escape into the gas phase.
- This process is the opposite of deposition, where a gas directly changes into a solid without passing through the liquid state.
- Sublimation is observed in certain substances that have a high vapor pressure at or below room temperature, such as dry ice (solid carbon dioxide), mothballs (naphthalene), and camphor.
- In the case of dry ice, it sublimes at a temperature of -78.5°C, producing carbon dioxide gas.
- Sublimation is an endothermic process, as it requires the input of energy to overcome the intermolecular forces holding the particles together in the solid state.
- The reverse process of sublimation, where a gas changes directly into a solid, is known as deposition.
- Sublimation has various applications, such as freeze-drying food, preserving sensitive materials, and purifying substances.
- Unlike chemical changes, physical changes are reversible, and the substance retains its original chemical composition after the change.

Conclusion:
- Among the given options, sublimation is the only physical change.
- Oxidation and reduction are chemical changes that involve the transfer of electrons.
- Decomposition is also a chemical change where a compound breaks down into simpler substances.
- Therefore, the correct answer is option C, sublimation.