How can you explain the ability of bodies to change their volume? Can we say that the volume of a gas

How can you explain the ability of bodies to change their volume? Can we say that the volume of a gas in a vessel is equal to the sum of the volumes of its molecules?

1. Bodies change their volume under the influence of temperature or, for example, under external influence. When the temperature rises, the body expands, for example, water becomes larger in volume when heated. Gas can also expand as the temperature rises, but its volume can be changed by performing mechanical work – compressing the gas under pressure. As the temperature rises, the average distance between the molecules of the substance increases, therefore the volume of the heated body also increases.

2. No, it is not equal, since the molecules are not located close to each other, but are at a distance from each other. Therefore, the volume of gas in the vessel is much larger than the total volume of the molecules of its constituents.