A gas is the third state of matter, where inter-molecular bonds are few and far between. This means that gas molecules are free to move around, rotating, vibrating, and translate themselves through space. Gasses are usually invisible, which means that many people may not know if a particular gas is present, as well that many gasses cannot be easily distinguished from one another.
The most common and plentiful gas in our world is not, as on would think it, air. Air is a term we use to describe the compilation of gasses that allow our bodies to function. The most plentiful gas in this mixture is gaseous nitrogen, which while not harmful to the human body, is not one of the more essential gasses to humans as a species. Nitrogen makes up about 80% of everyday air.
One of the most needed gasses in our air is oxygen, which is essential for human life. When we breathe, it is the oxygen that our bodies need to function properly. Oxygen is needed for combustion reactions, including those that occur in our bodies each and every minute of each and every day. For example, our bodies burn food by adding oxygen to it, which triggers a chemical reaction. For example, the combustion of glucose is what our bodies use to create adenosine triphosphate, commonly referred to as ATP. Our bodies use this ATP as energy to fuel our actions. This entire process would not be possible without the presence of oxygen.
Another common gas in our lives is hydrogen, which is extremely potent as an explosive. The famous explosion of the Hindenburg was caused by hydrogen gas, which was being used as fuel. Needless to say hydrogen is not a common fuel source anymore, but it still has widespread applications, particularly in the processing of consumer-grade foodstuffs.
Our world is fundamentally dependent on gasses. Everything from the most basic human body functions to the processes that industry uses to manufacture most of our modern conveniences. The nature of a gas is a mystery that has always aroused the curiosity of scientists, because of the amazing properties held by something that feels so intangible. It is part of the human condition to be curious, and hundreds of researchers have devoted countless hours of study to understanding the unknown, the intriguing, the unnoticeable. Even with all of our modern scientific knowledge, we do not fully understand how every gas in our world interacts with it, and such is the journey of scientific discovery.