What happens to the density of water when it freezes into ice?

What happens to the density of water when it freezes into ice?

• A. Ice becomes less dense than liquid water, which is why it floats.
• B. Ice becomes more dense than liquid water, which is why it sinks.
• C. Ice has the same density as liquid water.
• D. Ice dissolves in water, changing density.

Answer: (A)

Density is mass per volume, and water behaves unusually when it freezes. As liquid water cools and forms ice, the hydrogen-bonded molecules arrange into a crystal lattice that takes up more space. This expanded structure means ice has a lower density than liquid water (about 0.92 g/cm³ for ice versus ~1.00 g/cm³ for liquid water near 0–4°C). Because an object with lower density than its surroundings floats, ice sits on top of liquid water. That’s why water bodies freeze from the top and ice floats. The other options don’t fit because ice does not become denser, nor does it have the same density as liquid water, and it does not dissolve in the water.

Density is mass per volume, and water behaves unusually when it freezes. As liquid water cools and forms ice, the hydrogen-bonded molecules arrange into a crystal lattice that takes up more space. This expanded structure means ice has a lower density than liquid water (about 0.92 g/cm³ for ice versus ~1.00 g/cm³ for liquid water near 0–4°C). Because an object with lower density than its surroundings floats, ice sits on top of liquid water. That’s why water bodies freeze from the top and ice floats. The other options don’t fit because ice does not become denser, nor does it have the same density as liquid water, and it does not dissolve in the water.