In which state of matter do the particles spread apart and fill all the space available to them?
a. crystal
b. liquid
c. gas
d. solid

The correct answer is c) gas.

In gases, in fact, particles are not bound together (and the intermolecular forces between them are negligible) and they are completely free to move. For this reason, when a gas is put in a container, the particles of the gas will move in every possible direction, filling all the space available in the container (for this reason, we also say that gases have no fixed shape).

As newton's first law states a object in motion stays in motion

Then the answer would be d then