What are gases?
According to John Daintith, " Gas: A state of matter in which the matter concerned occupies the whole of its container irrespective of its quantity.in In an ideal gas, which obeys the gas laws exactly, the molecules themselves would have a negligible volume and negligible forces between them."

Gases are two natural gases found in nature and man-made industrial gases so that natural gases are two types:
Elemental gases: These gases are prepared with the materials found in the Earth and the rest of the other planets so that they are composed of atoms of only one element of the most prominent examples of hydrogen (H2), oxygen (O2) and nitrogen (N2),. Noble gases are also natural gases in the atmosphere, while chlorine (Cl2) and fluorine (F2) are present in composite materials,. Noble gases such as helium, argon, radian and neon That is, they exist in the form of single atoms.

Compound gases: These gases are formed in nature through chemical and biological processes, but differ because it consists of two or more elements to be a mixture of carbon, oxygen, nitrogen, hydrogen, nitrogenhydrogen, Ex: carbon-dioxide (CO2), methane (CH4).