Why is oxygen called gas?

Oxygen is called a gas because it exists in a gaseous state at standard temperature and pressure (STP), which are commonly used reference conditions for gases.

Standard temperature and pressure (STP) are defined as:

Standard Temperature: 0 degrees Celsius (32 degrees Fahrenheit) or 273.15 Kelvin.
Standard Pressure: 1 atmosphere (atm) or 101.3 kilopascals (kPa).
At STP, most elements and compounds, including oxygen (O2), exist as gases. This means that oxygen molecules are in a state where they have enough kinetic energy to overcome the attractive forces between them, allowing them to move freely and occupy the entire volume of the container they are in. In this gaseous state, oxygen can mix with other gases and is essential for respiration, combustion, and many chemical reactions.

It's important to note that elements and compounds can exist in different states of matter (solid, liquid, or gas) depending on the temperature and pressure conditions. Oxygen, for example, can exist as a solid (frozen oxygen) at very low temperatures and as a liquid at intermediate temperatures and pressures. However, at room temperature and standard atmospheric pressure, it is most commonly encountered as a gas, hence the term "oxygen gas."