Here's why:

* Positive and negative charged particles: Plasma consists of ions (atoms that have lost or gained electrons, giving them a net positive or negative charge) and free electrons.

* No volume or shape: Plasma doesn't have a fixed volume or shape like solids or liquids. It expands to fill its container, much like a gas.

While plasma does have particles, the definition doesn't specify that they have no volume or shape. It's more about the behavior of the particles within the plasma state.