Gas Physical Characteristics
 All gases can flow, like liquids. This means the molecules move about independently of each other. The majority of gases are colourless, like Hydrogen. Gas particles will spread about, or diffuse, in order to fill all the space in any container such as a bottle or a room. Compared to liquids and solids gases have a very low density and viscosity. We cannot directly observe most gases since they are without colour, however it is possible to measure their density, volume, temperature and pressure.