[The Scientist (OP)]

Please provide explanations. Thanks!

[Carbonizer]

The litre of water weighs more, and this is why ice floats in water. When water freezes, it expands and becomes becomes less dense. While it is true that most things are more dense in their solid state, it is not true of water.

[JaneMiller]

I agree with Carbonizer. Water is heavier

[Bill S]

Would this distinction hold in zero gravity?
I would think not, but I've been wrong before.

[chiralSPO]

Would this distinction hold in zero gravity?
I would think not, but I've been wrong before.

I think you are correct.

1 L of water is more massive than 1 L of ice. This will translate into greater weight if any force is applied to the samples.

[wolfekeeper]

It depends. A litre of ice can have a density of 1.65 times that of normal water, so I'm going with ice, unless it's specified to be at normal pressure, in which case it's water that is denser:

https://en.wikipedia.org/wiki/Ice_VII

[evan_au]

This chart suggests that even at -200C, ice is less dense than liquid water at 100C.
I assume that this is taken at standard pressure, so that no exotic phases of ice were present.
https://en.wikipedia.org/wiki/File:Density_of_ice_and_water_(en).svg

[PmbPhy]

Would this distinction hold in zero gravity?
I would think not, but I've been wrong before.

Water would still be more dense so if you had a comnination of water and ice in a centrifuge aboard the ISS the ice would still float to the surface of the water. But since nothing weighs anything in a weightless environment they its meaningless as you said.