Chemistry of Gases and Applications

CFCs (chlorofluorocarbons) were widely used as refrigerants in refrigerators and air conditioners due to their excellent heat transfer properties. They were phased out after being identified as major ozone-depleting substances under the Montreal Protocol. TVs and tube lights don't use CFCs, and cooking gas (LPG) is a fuel, not a refrigerant.

Helium is used to fill balloons because it is much lighter than air, making balloons buoyant. Unlike hydrogen, helium is non-flammable and safe for use. Nitrogen, oxygen, and argon are either too heavy or reactive for practical balloon use.

Brass tarnishes due to hydrogen sulfide (H2S) in the atmosphere, which reacts with copper in the brass to form a dark copper sulfide layer. Oxygen causes slower oxidation, while carbon dioxide and nitrogen don't produce this characteristic discoloration.

Incandescent bulbs are filled with nitrogen or argon gas to prevent the hot tungsten filament from oxidizing and burning out quickly. Hydrogen would react with the filament, carbon dioxide would decompose, and oxygen would accelerate filament burning.

Deep sea divers breathing compressed air can experience nitrogen narcosis. Helium is substituted for nitrogen in breathing mixtures because it's inert and doesn't cause narcosis, allowing divers to work at greater depths safely.

Oxy-acetylene welding is the most common gas welding process, using oxygen and acetylene to produce a very hot flame (around 3,200°C). Other gases like argon are used in TIG/MIG welding but not as commonly in traditional gas welding. The combination of oxygen and acetylene is the standard answer for general welding gas questions.

Argon (Ar) is the most abundant rare gas in Earth's atmosphere, constituting about 0.93% by volume. Helium and neon are present in trace amounts, while xenon is extremely rare.

Hydrogen sulfide (H2S) acts as a reducing agent because it can donate electrons (sulfur is oxidized from -2 to higher oxidation states). Sulfur dioxide is actually an oxidizing agent in most reactions.

In automotive nitrous oxide systems (NOS is a brand name), multi-stage wet direct-port injection delivers nitrous and fuel directly to each cylinder, producing maximum power. 'Wet' means fuel is mixed with nitrous; multi-stage allows staged activation for better control. Direct-port is more efficient than single-port injection.

Nitrous oxide (N2O) is commonly called 'laughing gas' because it causes euphoria and laughter when inhaled. It was discovered by Humphry Davy and has been used as an anesthetic and in dentistry for its pain-relieving and euphoric effects.

Nitrous is a drug and like any drug can be emotionally habit forming. While there is no physiological addition to nitrous, it can lend itself to compulsive use.

This is the correct option. Ammonia is the poisonous gas released by microorganisms present in water after they use up the water's oxygen.

This is the correct option. In the tertiary treatment, ozone gas can be used to kill the disease-causing organisms.

Dinitrogen tetroxide is the chemical compound N₂O₄. It is a powerful oxidizer, highly toxic and corrosive. N₂O₄ is hypergolic with various forms of hydrazine, i.e., they burn on contact without a separate ignition source, making them popular bipropellant rocket fuels.

The number of molecules in a given mass is inversely proportional to the molar mass. Hydrogen (H2) has the lowest molar mass (2 g/mol), so 1 gram of hydrogen contains the most molecules (0.5 moles). Carbon dioxide (44 g/mol), oxygen (32 g/mol), and ammonia (17 g/mol) all have higher molar masses, meaning the same mass contains fewer molecules. For example, 10g CO2 is only 0.23 moles.