(a)  Positions of particles (atoms, molecules or ions) are fixed because of strong attractive forces betwen them.
(b)  Inter- particle distances remain largely constant (i.e., "rigid" structure), but atoms undergo vibration at a fixed position.
(c)  There are practically no empty spaces.

(a)  Positions of particles can change because of weaker forces among them, and particles interact intimately contacting with neighbors.
(b) Average inter-particle distances are maintained although particles can move around: molecules can undergo translational as well as rotational movements (i.e., "fluid") in addition to the vibrational movements.
(c) There are practically no empty spaces.

(a) Positions and interparticle distances change constantly, as they collide and recoil all the time. This is because kinetic energies of particles in Gaseous state are much higher than in Solid  or Liquid states.  It overcome attractive forces between molecules to break them apart.
(b) Each particle move independently. Extent of movements (rotational, vibrational, and  translational) are much greater than in the liquid. state.
(c) Plenty of empty spaces between particles ("compressible"). Tha average distance between particles  depends on the pressure .