Ice density relative to liquid water is best described as:

• A. Ice is denser than liquid water.
• B. Ice sinks in liquid water.
• C. Ice and liquid water have equal density.
• D. Ice is less dense than liquid water, so it floats.

Answer: (D)

Density determines whether something sinks or floats in a liquid. Water is unusual: when it freezes, the molecules form a crystal lattice with more open space, so ice becomes less dense than liquid water. Because its density is lower, ice floats on water (Archimedes’ principle: it displaces a volume of water equal in weight to the ice). If ice were denser, it would sink; if they had the same density, it would be neutrally buoyant. So the best description is that ice is less dense than liquid water, so it floats.