Chemistry of Gases and Applications

Calcium hydride is the chemical compound with the formula CaH₂. This grey powder (white if pure, which is rare) reacts vigorously with water liberating hydrogen gas. CaH₂ is thus used as a drying agent, i.e. a desiccant.

Spark ionization is a method used to produce gas phase ions from a solid sample. The prepared solid sample is vapourized and partially ionized by an intermittent discharge or spark.

A cold gas thruster is a rocket engine/thruster that uses a typically inert gas as the reaction mass. A cold gas thruster usually simply consists of a pressurized tank containing gas, a valve to control its release and a nozzle, and plumbing connecting them.

Pentaborane is a colourless mobile liquid with a strong pungent odour (resembling garlic, acetylene or sour milk). In the 1950s it was considered as a good prospect for rocket or jet fuel. Its chemical structure is that of five atoms of boron compounded with nine atoms of hydrogen (B₅H₉).

Hexanes are significant constituents of gasoline. They are all colourless liquids at room temperature with boiling points between 50 and 70 °C and gasoline-like odour. They are widely used as cheap, relatively safe, largely unreactive and easily evaporated non-polar solvents.

Early Earth had a reducing atmosphere composed mainly of methane, ammonia, hydrogen, and water vapor. Free oxygen was essentially absent because it reacts rapidly with reducing compounds and was only produced later by photosynthetic organisms.

Earth's primitive atmosphere was reducing in nature, containing methane, ammonia, hydrogen, and water vapor but lacking free oxygen. Free oxygen only accumulated after the evolution of photosynthetic organisms billions of years later.

The Moon lacks a significant atmosphere and cannot support life as we know it. While absence of oxygen (A) is one factor, the lack of liquid water, extreme temperature variations, and no atmosphere are also critical reasons. The question identifies oxygen as the key missing component.

Aerogel is a manufactured material with the lowest bulk density of any known porous solid. It is derived from a gel in which the liquid component of the gel has been replaced with a gas. The result is an extremely low-density solid, with a notable effectiveness as a thermal insulator.

Helium is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table.Helium is used in cryogenics (its largest single use, absorbing about a quarter of production), particularly in the cooling of superconducting magnets, with the main commercial application being in MRI scanners.

Xenon tetrafluoride is a chemical compound with chemical formula XeF₄. It was the first discovered binary compound of a noble gas. It is produced by the chemical reaction of xenon with fluorine.

This is not an air gas. This gas is a synthesis gas usually produced from the reaction of calcium carbide with water. Acetylene is a gaseous hydrocarbon. It has a strong garlic odor. The gas is colorless, unstable, highly combustible. Acetylene is used in machine/metal construction for cutting and welding (with oxygen). It is also used in the glass industry for lubrication of bottle production molds.

Cryogenic gas is a gas which has been supercooled such that it is a liquid or solid at a standard temperature.Cryogenic gases are liquefied gases at standard temperature and pressure. They are kept in their liquid state at very low temperatures. Cryogenic gases are very popular and they are used as fuels, oxidizers and refrigerants. These gases are to be stored properly to get their maximum usage.

Earth's atmosphere consists of approximately 78% nitrogen gas (N2), making it the most abundant atmospheric gas. This high percentage is crucial because nitrogen is essential for life, but most organisms cannot directly use atmospheric nitrogen in this form. The remaining atmosphere is primarily oxygen (21%), argon (0.9%), and trace gases including carbon dioxide (0.03%).

Hydrogen is the most abundant gas in the Sun, making up about 73% of its mass. Helium (B) is second at ~25%, while other gases like nitrogen (C) exist only in trace amounts. The Sun's energy comes from hydrogen fusion.