The right answer is 9%
Water is one of the very few elements to have a larger volume in the solid state than in the liquid state (for an equivalent mass, of course). Indeed, its liquid form consists of water molecules "in bulk". They are in contact with each other, but disordered.
When it solidifies, the molecules are organized into molecular cells. In the case of water, in hexagonal form. However, once the molecules are wisely arranged in hexagon, there is much more vacuum between them than when they were in the liquid phase, that is to say "glued" to each other. There is a variation of almost 9% of the volume. But be careful, do not confuse with the mass.
When water's temperature drops, its volume decreases until it reaches 4 degrees Celsius. As water freezes, its volume rapidly increases. The rate of increase can be calculated by dividing the difference between the volumes at these temperatures by the volume at 4 degrees.
