When molecules gain energy, which of the following is most likely to occur?

• A. They lose electrons and become negatively charged.
• B. They become chemically inert.
• C. Their particles move faster and may change phase.
• D. Their mass increases significantly.

Answer: (C)

Verified step by step guidance

1. Understand that when molecules gain energy, this energy typically increases their kinetic energy, meaning the molecules move faster.
2. Recognize that increased molecular motion can lead to changes in physical state (phase changes), such as melting, boiling, or sublimation, depending on the amount of energy absorbed.
3. Note that gaining energy does not cause molecules to lose electrons and become negatively charged; ionization requires much higher energy and specific conditions.
4. Understand that molecules do not become chemically inert simply by gaining energy; in fact, increased energy can make molecules more reactive.
5. Recall that the mass of molecules does not increase significantly when they gain energy, as mass is conserved; energy changes affect motion and phase, not mass.