When water freezes and becomes solid ice, the hydrogen bonds create a crystal structure and there is fixed space between each water molecule. This...

Density is the amount of mass per unit of volume. Most substances are more dense in their solid state than in their liquid state. This is because the particles of most substances become more closely packed in their solid state. 

Water particles are held together by intermolecular forces called hydrogen bonds. Hydrogen bonds occur between the positively charged side of one water molecule and the negatively charged side of another water molecule. When liquid water changes to a solid state, the hydrogen bonds between the water particles result in the formation of a crystal structure with spaces between the water particles. The additional space between the water particles cause solid water to be less dense than liquid water. Because ice is less dense than water, it floats on water. 

Therefore, the answer is b.