If you fill a glass to the brim with ice water and the ice melts, what will happen?

Answer 1

Since ice is known to be less dense than liquid water, a given mass or molar quantity will occupy more volume. Thus, as the ice melts, the more dense water will occupy less volume and the water level will be below the brim.

Answer 2

If you fill a glass to the brim with ice water and the ice melts, the amount of space needed for the liquid to expand will increase causing the liquid to overflow out of the glass. Even though there is space between the ice particles, as a solid, it still has less energy because it is not moving. However once it gains energy, it needs more space to move since it is going from a less energy state to a more energy state which means it will require more space.