Concept:The physical states of matter depend on the arrangement and interaction of their particles.
Explanation:In solids, particles are closely packed with strong intermolecular forces, giving a fixed shape.
In liquids, particles are less closely packed with weaker forces, so they flow but have a fixed volume.
In gases, particles are far apart with very weak forces, so they expand to fill any container.
Thus, the observed differences are due to the spacing and forces acting between the molecules.
Answer:C. the spacing and forces acting between the molecules