Which of the following describes the density of ice relative to liquid water?

• A. Ice is less dense than liquid water
• B. Ice is more dense than liquid water
• C. They have the same density
• D. Density varies with temperature

Answer: (A)

Ice floats on water because it is less dense than liquid water. Density is mass per volume, so a given volume of ice weighs less than the same volume of liquid water. When water freezes, the molecules arrange into a hexagonal lattice that creates more open space, making ice about 0.92 g/cm³ while liquid water near room temperature is about 1.0 g/cm³. This lower density is why ice rises to the surface.

Context helps: water’s density also reaches a maximum at around 4°C, so as water cools toward freezing it becomes slightly less dense, and freezing adds even more open structure, further reducing density. The result is ice that floats, which has important ecological effects like insulating ponds and allowing life to persist beneath the frozen surface.