* In a given volume: Solids have more particles than gases. This is because the particles in a solid are tightly packed together, while the particles in a gas are spread out.
* In a given mass: This is where it gets tricky. Gases can actually have *more particles* than solids of the same mass. This is because the particles in a gas are much lighter than the particles in a solid.
Here's an analogy: Imagine you have a bucket full of marbles (solid) and a balloon full of helium (gas). The bucket of marbles has more marbles in a given volume, but the balloon filled with helium has more *individual helium atoms* in the same weight as the marbles.
So, the answer really depends on what you're comparing!
