Final answer:
Solids have a definite shape and volume because the individual particles of a substance are in fixed positions with respect to each other, due to the lack of thermal energy to overcome intermolecular interactions.
Step-by-step explanation:
In the solid state, the individual particles of a substance are in fixed positions with respect to each other because there is not enough thermal energy to overcome the intermolecular interactions between the particles. As a result, solids have a definite shape and volume. Solids are rigid and do not fill their entire containers like gases, nor do they adopt the shape of their containers like liquids do. They also cannot be easily compressed like gases.