Earth, with roughly 78%.
animals
the Air
No. Too high of an oxygen concentration can have adverse effects on our health and presents a fire hazard.
The Dumas method is used to determine nitrogen concentration in compounds.
nitrogen
Nitrogen plant burns are caused when to much fertilizer (or fertilizer with a high concentration of Nitrogen) is added to a plant. If the concentration of Nitrogen (or Nitrogen compounds such as ammonia) is to high it causes the soil to become highly acidic in the area where it was applied, the high acidity damages (or kills) the roots of the plant retarding or preventing the uptake of water or nutrients by the plant.
The greatest concentration of nitrogen on the Earth is found in its atmosphere. The atmosphere is approximately 78 percent nitrogen.
Other planets do have oxygen, but not in as high of concentration as we have here on Earth.
Uranus.
The lowest concentration of nitrogen can be found in the urine when it is first produced. As it accumulates in the bladder, so does the overall concentration of nitrogen.
Both compounds are toxic and can be lethal at high concentration.
Assuming you mean a concentration of 0.023 as a mole fraction... 0.023 is equivalent to 23000 ppm
Chicken feces contains a high concentration of uric acid (the white part) This is high in nitrogen and a basic need in all gardens.
animals
Earth, Mars and venus all have nitrogen and Carbon dioxide in their atmosphere, though the levels vary from planet to planet.
An area of higher concentration to an area of lower concentration.
Pluto