What is the main difference between gas and solid states of matter?

The main distinction between the gas and solid states of matter lies in the properties of shape and volume. Solids have a definite shape and volume, meaning they maintain their form and do not change based on the container they occupy. This rigidity is due to the closely packed arrangement of particles in solids, which are held together by strong intermolecular forces.

In contrast, gases do not have a defined shape or volume; they will expand to fill the entire space available to them. The particles in gases are much farther apart and move freely, which allows the gas to take the shape of its container.

The concept of definite shape and volume is crucial to understanding the behavior of matter in different states, making option C the accurate choice.