Apentix/AP Biology/Unit 1: Chemistry of Life/Question
AP Biologyeasymcq1 pt

Ice cubes float in a glass of water rather than sinking. Which explanation is correct?

A.Hydrogen bonds lock molecules into an open hexagonal lattice that is less dense than liquid water
B.Cold water contracts so much that ice becomes heavier per unit volume
C.Air bubbles trapped during freezing provide all of ice's buoyancy
D.Frozen hydrogen bonds become stronger and pull the molecules downward

Explanation

Core Concept

As water freezes, each molecule settles into hydrogen-bonded positions about four neighbors strong, holding molecules farther apart than the constantly shifting, rebonding arrangement of the liquid. The spread-out lattice occupies more volume per molecule, so ice's density drops below that of liquid water and it floats. Lakes therefore freeze from the top down, insulating aquatic life underneath through winter.

Correct Answer

AHydrogen bonds lock molecules into an open hexagonal lattice that is less dense than liquid water

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