(a) Solids have a definite shape to them. Liquids do not have a definite shape. Gases do not have a definite shape. The intermolecular space between solids is absent. (b) Rigidity refers to a substance’s resistance to changing shape, compressibility is its ability to be compressed, and fluidity is its ability to flow. Filling a gas container means the gas takes the shape of the container. Shape refers to the definite boundary of an object. Kinetic energy is the energy of motion, and density is mass per unit volume.
Elaboration:
Rigidity:
Solids are generally considered highly rigid because they resist deformation when an external force is applied. Liquids and gases have lower rigidity.
Compressibility:
Gases are highly compressible, meaning their volume can be significantly reduced under pressure. Solids and liquids are relatively incompressible.
Fluidity:
Liquids and gases are considered fluids because their particles are free to move past each other, allowing them to flow. Solids do not have fluidity.
Filling a gas container:
Gases fill a container because their particles are free to move and spread out, taking the shape of the container.
Shape:
A shape is the defined boundary or outline of an object. Solids have a definite shape, while liquids and gases take the shape of their container.
Kinetic energy:
Kinetic energy is the energy associated with the motion of particles. Gases have the highest kinetic energy, followed by liquids, and then solids, as their particles move at varying speeds.
Density:
Density is a measure of mass per unit volume. Solids generally have the highest density, followed by liquids, and then gases.