What does Atm stand for?

Atm stands for Atmosphere, which is a unit of pressure. It is commonly used in various fields, including meteorology and medicine, to describe air pressure or the pressure exerted by a gas in a given volume. One atmosphere is defined as being precisely equal to 101.325 kilopascals (kPa) or approximately 14.7 pounds per square inch (psi) at sea level at 15 degrees Celsius. In the context of medical gas administration and respiratory therapy, understanding the concept of atmospheric pressure is crucial, especially when working with gases that may be administered to patients, such as oxygen or nitrous oxide.

The other options, while related to scientific terminology, do not pertain to atmospheric pressure. Atomic mass refers to the mass of a chemical element’s atoms, atomic molecule does not represent a standard scientific term, and atmospheric mercury is not a recognized unit of pressure. Thus, the correct option, Atmosphere, encapsulates the standard measure of pressure relevant to the question.