Most substances become denser when frozen, but water becomes less dense. As a consequence, ice floats. What is responsible for this unusual property?

Question

A) As the temperature drops and water molecules slow down, there is increasing opportunity for the hydrogen bonds to form. These bonds hold the numerous V-shaped molecules slightly farther apart than when no hydrogen bonds exist, causing the water to be less dense.
B) Oxygen is able to covalently bond with additional hydrogen molecules when the temperature drops and molecular motion slows down. Because hydrogen floats, the greater the number of hydrogen atoms bound to an oxygen molecule, the more buoyant it becomes.
C) Because covalent bonds are broken by the process of freezing, ice molecules have fewer electrons than water, and so they are less dense and float.
D) Most water molecules have some sodium and chloride ions bound to them. Upon freezing, the sodium and chloride ions are lost, making the ice less dense.
E) Molecular motion is slower in solid substances than liquids; therefore, more of the molecules can evaporate. As a consequence, when water freezes, it stays in close contact with air.

Answer 1

A) As the temperature drops and water molecules slow down, there is increasing opportunity for the hydrogen
bonds to form. These bonds hold the numerous V-shaped molecules slightly farther apart than when no hydrogen bonds exist, causing the water to be less dense.