Here's why:

* Mass is a measure of the amount of matter in an object. It's a fundamental property.

* The state of matter (liquid, solid, or gas) depends on the arrangement and movement of the molecules. The amount of matter in an object doesn't change just because its state changes.

Example:

* A block of ice (solid) will have the same mass as the water (liquid) it melts into.

* A balloon filled with air (gas) will have less mass than the same volume of water (liquid).

Important Note:

* While the *mass* remains the same, the *density* changes significantly between states of matter. Density is mass per unit volume, and the molecules are packed more tightly in solids than liquids, and more loosely in gases.