At room temperature, all samples of liquid water must have the same 1.mass 2.density 3.volume 4.weight

The answer is 2. density

At room temperature, all samples of liquid water must have the same density.

Whatever the volume of different liquid water samples, they always have same density. As density of liquid water is always same that is 1 g cm⁻³. So different liquid water can have different volume, weight and mass but their density always remains same.