Question

Why does ice float after it crystallizes?

Answer 1

C. Its density is less than water
This is why. The denser the object is the farther it sinks. Since crystallized ice floats it is less dense than the surrounding liquid.

Answer 2

Crystallized ice has larger volume but the mass remains constant so density reduces by the equation Density = Mass/Volume.
As it is being less dense, it floats.