Which statement best describes how the individual molecules in water vapor differ from those in liquid water?

• A. They are farther apart
• B. They are closer together
• C. They move more slowly
• D. They have stronger intermolecular forces

Answer: (A)

Molecules in water vapor are farther apart. In the gas state, water molecules spread out to fill the space available, move rapidly, and interact only weakly with each other, so the average distance between them is large. In liquid water, the molecules are closer together and held by stronger intermolecular forces, which keeps them more compact and densely packed. So the statement that best describes the difference is that the molecules in water vapor are farther apart.

The other ideas don’t fit: in liquid water the molecules are not closer together than in vapor, they are; gas molecules don’t move more slowly than in liquid—they move faster; and gas does not have stronger intermolecular forces than liquid water.