ANSWER:

The compressed natural gas or CNG was made by COMPRESSING natural gas under standard atmospheric pressure. This CNG is distributed in cylindrical tank. It is used as a fuel in automobile industries and household processes. It is also used in vehicles as a fuel.

Apart from LNG (liquefied natural gas), CNG is in gaseous form inside the cylinder but the LNG is in liquid form inside the cylinder. When LNG comes out from the cylinder it is in gaseous form but CNG is in gaseous form when it is inside and outside the cylinder. CNG is less expensive than LNG but the mass of gas inside the CNG cylinder is LESSER than LNG.

And the question here is what happens between the molecules of CNG when the cylinder of CNG is slowly used. When the cylinder of CNG is slowly used up, the DISTANCE between the molecules of CNG will increase. The molecules of CNG will move apart from each other and fill the cylinder. We know that CNG is filled in the cylinder as compressed natural gas inside the cylinder, when it is slowly used up there will be space increasing between the CNG molecules to move somewhat freely than before inside the cylinder as it is present in gaseous form. Gaseous molecules tend to move freely when they get more space. So when some of the gaseous molecules goes out then the other molecules get free space and they move freely inside it.