I told my chemistry teacher I wanted to study volatile compounds.

This joke gets its comedic bang from a clever bit of wordplay, specifically using the dual meanings of "volatile" and "gas." When the student says they want to study "volatile compounds," they're referring to substances that easily evaporate or change into a gas. However, "volatile" also carries the meaning of being unstable, dangerous, or even explosive, hinting at the potential hazards of working with such chemicals.

The punchline then takes this chemical concept to a darkly humorous and absurd extreme. When the teacher warns that the last student "became a gas," it plays on the literal transformation of a substance into a gaseous state, but it's also a morbidly funny euphemism for something far more permanent and unfortunate happening to the previous student. It's an exaggerated take on laboratory safety and the potential consequences of mishandling chemicals.

The humor comes from this unexpected twist, combining scientific terminology with a dramatic, albeit impossible, outcome for a person. It's a lighthearted jab at the serious nature of chemistry, reminding us that while volatile compounds are fascinating, they also demand respect and careful handling, just not usually to the extent of turning researchers into thin air.