Here's why:
* Matter is anything that has mass and takes up space. Gases are matter, so they must have mass.
* Mass is a measure of the amount of matter in an object. Even though gases are spread out and invisible, they are still made up of tiny particles (atoms or molecules) that have mass.
* The mass of a gas can be measured. We can use scales, balances, or other techniques to determine the mass of a gas, although it can be trickier than measuring solids or liquids.
For example:
* The air we breathe has mass. You can feel this when the wind blows; it's the mass of the air that exerts pressure.
* A balloon filled with helium has mass. You can weigh it before and after filling it to see the difference in mass.
Important Note: While gases have definite mass, they don't have a definite volume like solids or liquids. Gases expand to fill their container.
