Which statement correctly defines matter?

The definition of matter encompasses anything that has mass and occupies space. This means that any physical substance, whether solid, liquid, or gas, falls under this classification. The concept of mass is fundamental because it relates to the amount of matter present in an object, which is a key characteristic of all physical substances.

While other options touch on aspects related to matter, they do not fully encompass its definition. For example, changing states refers to the physical states of matter (solid, liquid, gas), but not all matter necessarily changes states. The ability to be observed through the senses is limited to certain forms of matter and does not apply to all characteristics, such as microscopic matter or elements like gases that may not be easily perceived. Lastly, restricting the definition of matter solely to substances in liquid form excludes solids and gases, which are also fundamental types of matter. Thus, the statement that correctly defines matter is that which emphasizes its possession of mass.