When water molecules change from solid to liquid, which of the following best describes what happens at the molecular level?

• A. The water molecules break apart into hydrogen and oxygen atoms.
• B. The hydrogen bonds between water molecules weaken, allowing the molecules to move more freely.
• C. The water molecules form stronger ionic bonds.
• D. The water molecules lose all intermolecular forces.

Answer: (B)

Verified step by step guidance

1. Understand the states of matter: In a solid, water molecules are held closely together in a structured arrangement primarily due to hydrogen bonding, which is a type of intermolecular force.
2. Recognize that when water changes from solid (ice) to liquid (water), the process is called melting, which involves an increase in molecular motion and energy.
3. Identify that during melting, the hydrogen bonds between water molecules do not break completely but weaken enough to allow the molecules to move past each other more freely, transitioning from a rigid structure to a fluid one.
4. Note that water molecules do not break apart into individual hydrogen and oxygen atoms during melting; the molecular structure (H₂O) remains intact.
5. Conclude that the correct molecular-level description is that the hydrogen bonds between water molecules weaken, allowing increased molecular mobility, rather than forming stronger ionic bonds or losing all intermolecular forces.