Why is Hydrogen called inflammable air?

Hydrogen is sometimes referred to as "inflammable air" because it is highly flammable and combustible in air. The term "inflammable" means capable of being easily ignited and burned. Hydrogen, in its gaseous form, is highly reactive and can readily combine with oxygen in the air to produce water vapor while releasing a significant amount of heat.

The term "inflammable air" was used historically to describe gases that could easily catch fire, and hydrogen fits this description perfectly. It was first discovered and studied in the late 18th century, during the period when scientists were actively exploring gases and their properties. Eventually, it was understood that hydrogen, despite being lighter than air, could indeed ignite and burn, hence the term "inflammable air" became associated with it.