free oxygen
Technical term in chemistry for oxygen not combined with other elements; used in contexts like radical chemistry, water quality, and biochemistry.
Free oxygen is studied as a type of reactive oxygen species.
活性酸素 (reactive oxygen) is a broader category that includes free radicals like superoxide; 遊離酸素 specifically refers to oxygen in its uncombined, often radical form.
Compound of 遊離 (yūri, 'free, uncombined') and 酸素 (sanso, 'oxygen'). The term is a direct calque from English 'free oxygen' used in chemistry.