मानवांमध्ये, श्वास सोडलेल्या हवेमध्ये सुमारे ________ ऑक्सिजन असतो.

Inhaled air has about 21% oxygen. The body absorbs only part of it, so exhaled air still contains about 16% oxygen, along with about 4% carbon dioxide; this is why mouth-to-mouth resuscitation works.