Which statement about phase changes is true?

• A. Melting is exothermic.
• B. Condensation requires energy input.
• C. Deposition requires energy input.
• D. Sublimation occurs when a solid changes directly to a gas, absorbing energy.

Answer: (D)

Phase changes involve energy transfer: some changes require energy from the surroundings, while others release energy. Melting and vaporization absorb energy to break intermolecular attractions, so they are endothermic. Condensation and deposition release energy as particles become more ordered and form stronger interactions, so they are exothermic.

Sublimation is the process where a solid changes directly into a gas, bypassing the liquid phase, and it requires energy input to overcome the solid’s lattice and pull particles into the gaseous state. That’s why sublimation is the true statement. For example, dry ice (solid CO2) sublimates at room temperature, turning directly into CO2 gas as it absorbs heat.

The other statements are inconsistent with how phase changes involve energy: melting is not exothermic, condensation does not require energy input, and deposition does not require energy input.