What term did Joseph Priestley use for the isolated oxygen gas?

• A. Phlogisticated air
• B. Dephlogisticated air
• C. Vital air
• D. Oxygen

Answer: (B)

The term reflects how Priestley described his discovery within the old phlogiston framework. He believed air contained phlogiston, and the gas he isolated had been freed of it, so he called it dephlogisticated air. This naming emphasizes that, in his view, the gas was air deprived of phlogiston, which is why it could support life and combustion. Later chemists renamed it oxygen, but Priestley’s label captures how the gas was understood at the time. The other phrases aren’t the specific designation he used for the isolated gas, and oxygen is the modern term that replaced his terminology.