Nitrogen and Oxygen in Atmosphere - Class XI

During the process of photosynthesis, the hydrogen is combined with carbon atoms to produce oxygen which is then released into the atmosphere.

Oxygen is not present in graphite. It is am allotrope of carbon. 

Plant is necessary for animals for food and shelter,air is important for atmosphere and oxygen is important for breathing.

Plants consumes carbon dioxide and gives oxygen.

The percentage of oxygen in an atmosphere is maintained by consumption of carbon dioxide by plants and consumption of oxygen by living beings.

Water can be found in liquid form in oceans, rivers, lakes and rain; in solid form in ice and snow; and as a gas (water vapour) in the atmosphere.

NITROGEN is used as a refrigerant. Nitrogen is a liquid at temperatures below 196.5 C and is used as a refrigerant for such things as preservation of blood and cooling of large computer systems, as well as some industrial uses. Being a liquid, it is more convenient to use for low temperature cooling than dry ice. Liquid nitrogen is also used in oil wells to build up pressure in order to force crude oil upward.

Oil and fat containing food items are flushed with nitrogen because the food containing fats and oil become rancid after sometime because of oxidation and give smell having a bad taste. Presence of nitrogen helps food to save from rancidity.

Lime water turns milky when exposed to air and stirred as lime water mixes with $CO _{2}$ and forms $CaCO _{3}$ (calcium carbonate) which turns the lime water milky.