Sorry for taking so long to answer this.
Liquid contains particles (atoms, molecules or ions). These particles practically stay there and are unchanging as long as it doesn't evaporate quickly. If the number of particles are the same, it would make sense that the volume would remain the same too.
Liquids have their particles weakly interacting. The intermolecular forces that binds them like glue is strong enough to prevent them from escaping but is not strong enough to hold them in place. Therefore, liquids have no definite shape. They take the shape of the container it is in.