__Oxygen__ has the atomic number 8, meaning its nucleus has 8 protons. The number of neutrons varies according to the isotope: the stable Isotopes of oxygen have 8, 9, or 10 neutrons - wikipedia

The air we breath is made up of about 78% Nitrogen and 20.9% Oxygen. The last 1.1% is basically Argon, with a bit of Helium, Neon, and Carbon Dioxide. Ideally humans should only breathe air with 19.5% to 23.5% Oxygen content - psu.edu

YOUTUBE uql9B93h1Xc Can I Die From Too Much Water? Blood? Oxygen? We all know that we need things like water and oxygen to live, but what happens when you get too much of a good thing?

Oxygen is a member of the chalcogen group on the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other chemical compounds.

By mass, oxygen is the third-most abundant element in the universe, after hydrogen and helium. At standard temperature and pressure, two atoms of the element chemical bond to form dioxygen, a colourless and odourless diatomic gas.

Diatomic oxygen gas constitutes 20.8% of the Earth's atmosphere. As compounds including oxides, the element makes up almost half of the Earth's crust.

Oxygen. Chemical element with atomic number 8 - wikimedia

Dioxygen is used in cellular respiration and many major classes of organic molecules in living organisms contain oxygen, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone.

Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms.

Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms.

Another form of oxygen, ozone, strongly absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of smog and thus a pollutant.

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# References - https://sciencing.com/minimum-oxygen-concentration-human-breathing-15546.html - https://www.scientificamerican.com/article/the-oxygen-dilemma/