Final answer:
Solid and liquid states have similar densities due to particles being in close contact, whereas gas state has a much lower density because particles are spread out.
Step-by-step explanation:
The densities of a material in its solid and liquid states are similar because the atoms, ions, or molecules are in close contact in both states. This proximity of particles results in a similar arrangement whether the substance is a solid or liquid, hence they both have definite volumes and are incompressible. However, in the gas state, the distance between neighboring molecules is much greater, with these particles spreading out to fill their container, leading to a much lower density than in the liquid or solid states.