What is matter defined as?

Matter is fundamentally defined as anything that has mass and occupies space. This definition encompasses all physical substances in the universe, including solids, liquids, and gases. The key components of this definition are mass, which relates to the amount of matter in an object, and volume, which is the space that the object occupies. This understanding is critical in fields such as physics and chemistry, as it sets the foundation for more complex concepts related to the behavior and interactions of different materials.

The other choices, while they contain elements of truth about certain aspects of matter, do not fully capture the complete and precise definition. For instance, while substances can indeed exist in solid, liquid, or gas forms, this description is more about the states of matter rather than defining what matter is. Observing matter through the senses relates to perception rather than defining the intrinsic properties of matter itself. Similarly, stating that matter is a collection of atoms focuses solely on the atomic composition, which does not universally apply to all forms of matter, particularly those that may not be structured solely as 'collections' of discrete atoms. Thus, the first option offers the most accurate and encompassing definition.