Chemistry And Sustainability Concepts For STEM Students Practice Test

Which statement best describes why ice floats on water?

Ice is less dense than liquid water. Ice is more dense than liquid water. Ice has the same density as water. Ice dissolves in water.

Correct Answer:

Ice is less dense than liquid water.

Explanation:

The key idea here is density and buoyancy: something floats when its density is less than the liquid around it. Ice floats on water because the solid form is less dense than liquid water. When water freezes, water molecules arrange into a hexagonal lattice held by hydrogen bonds, creating more open space and a lower density (about 0.92 g/cm³ for ice versus ~1.00 g/cm³ for liquid water at typical temperatures). Because ice is lighter per unit volume than the surrounding water, the buoyant force pushes it upward, causing it to float. If ice were denser than water, it would sink; if it had the same density, it would neither float nor sink distinctly. The idea isn’t about dissolving; it’s about how density differences drive buoyancy.

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