The different characteristics as elaborated in CBSE Class 9 Science Chapter 1 solutions are based on six parameters - (1) Shape, (2) Volume, (3) Rigidity or Fluidity, (4) Intermolecular force, (5) Intermolecular space, and (6) Compressibility. Few of the characteristics as mentioned in Matter in Our Surroundings Class 9 NCERT solutions indicate that solids are of a fixed shape, volume and rigid but liquid is without fixed shape or volume, and it is less rigid than solid. On the other hand, gas neither has any fixed shape or volume, nor is it rigid.