Question

what is Percentage of Nitrogen in ground Air . does it increase or decrease when one Climbs Mount Everest?​

Answer 1

The atmosphere is a Homosphere,ie, uniform composition of gases(78%N 21%O, 1%other) at most heights except for ground but that's because of human activities like carbon emissions from cars.

We commonly hear that at high altitudes oxygen level decreases, Thats somewhat true, but the levels of other gases also decreases. The composition remains same, but the air gets 'thinner', in other words, density decreases.

Hope it helps.

Answer 2

Earth’s oxygen is produced by the ocean:

Ever stopped to think where oxygen comes from? Your first thought may be a rainforest, but marine organisms take the bait. Plankton, seaweed and other photosynthesizers produce over half of the world’s oxygen