Which statement best describes the atoms in a gas? they vibrate in place. they stay in a fixed position. they are closely packed. they move freely in all directions.

            Option-D : They move freely in all directions.

                   The physical properties of gases are well explained by Kinetic Molecular Theory. The key postulates of this theory are;

                              1) Composition: Gases are made up of small particles called molecules. The size of these molecules is very small as compared to the distance between molecules, therefore the actual volume of molecules is taken negligible as compared to volume occupied by them.

                             2) Intermolecular Forces: All the gas molecules present in a container behaves independently because they have no force of interactions between them Hence, the attractive forces are taken negligible or too little.  

                              3) Energies: Gas molecules have greater kinetic energy as compared to solids and liquids. Hence, The gas molecules move randomly. They collide with each other and with the walls of the container which causes pressure.

                  Therefore, due to large spaces, no interactions, small sizes and high energies the gas particles move freely and there position is not stationary.