How do you tell if the sample of matter is solid, liquid or gas?

There is one simple way to determine between solids, liquids, and gases. Are you able to move the substance? And if you are, how does it move? If it takes on the shape of its new container, it is a liquid. For example, if you pour water from a cup into a bowl, it will fill the bowl, not stay in the same shape as it was in the cup. However, if you put a marble in a cup and then pour the marble into the bowl, it will remain the same shape, and is therefore a solid. If you move a gas into a container, and the container is not sealed, it will not remain in the same shape.

Solid - the substance does not change depending on the container. It has a rigid and unmoving structure.

liquid - the substance maintains its volume, but assumes the shape of the container.

gas - the substance assumes the entire volume AND shape of the container.