In non biological fixation of nitrogen when the plant dies the fixed nitrogen is released making it available to other plants and this helps to fertilize the soil. The great majority of legumes have this association but a few genera do not. In farming practices fields are rotated through various crops like clover and buckwheat which are known as green manure.

By the use of Haber process, fixation of nitrogen can be done artifically.

Phosphate rock is too insoluble for direct use, and is commonly treated with sulfuric acid to make a mixture of calcium sulfate and the more soluble calcium hydrogen phosphate, called superphosphate.The use of superphosphate usually supplies adequate calcium. 

Nitrogen fixation is a process in which nitrogen(N₂) in the atmosphere is converted into ammonia (NH₃) and useful compounds. Atmospheric nitrogen or molecular dinitrogen (N₂) is relatively inert: it does not easily react with other chemicals to form new compounds.

Isotope of oxygen is used to detect the reaction mechanism of formation of esters. 

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.

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.

$71\%$ of the earth's surface is covered with water. Hence, earth is also known as the Blue Planet.

A glass of water is fit for drinking. Water in a pot may contain impurities like dust, sand, etc. Sea contains huge number of impurities including huge levels of salts and water with bacteria and chemicals and is not preferred for drinking. 

About three-fourth of the Earth's surface is covered with water, i.e., about $71\%$ of the earth's surface has water in it.  

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.

Distilled water is not a form of natural water. It is one of the form of purified water.

The water is collected from all of the above natural sources i.e lakes, rivers, ponds, and wells.

The approx. percentage of water human body is $70\%$. The average adult human body is $50-65\%$ water, averaging around $57-60\%$. The percentage of water in infants is much higher, typically around $75-78\%$ water, dropping to $65\%$ by one year of age. Body composition varies according to gender and fitness level because fatty tissue contains less water than lean tissue. 

Water covers over 70% of the earth's surface.

Water occurs in both free and combined state. In free state in the form of lakes, rivers and in the combined state in the form of body fluids.

Human body contains approximately 70% of water.

Water occurs in oceans in maximum amount.

Fruits and vegetables contain large quantities of water in proportion to their weight. When these foods are eaten, the water can be absorbed by the body. These water found in Vegetables in combined state.

Most of this water present on earth in different sources is not fit for human consumption. The water that is fit for use is freshwater. 

About $71\%$ of earth's surface is covered by water.

A falling of rain on earth causes breaking up of rocks and transferring their minerals to the ocean, the ocean becomes saltier and by evaporation, water evaporates leaving salt in the oceans.

Almost all the water on the earth is contained in the oceans, seas, rivers, lakes, ice caps, as ground water and in atmosphere as water vapour.

Perennial rivers flows continuously throughout the year irrespective of seasons. Mostly they originates from the mountain and water is fed by melting of glaciers. These river get water by rain in rainy season, melting of ice in summer and by snow in winter.

In a flame of pure hydrogen gas, burning in air, the hydrogen (H$ _2$) reacts with oxygen (O$ _2$) to form water (H$ _2$O) and releases energy. If carried out in atmospheric air instead of pure oxygen, as is usually the case, hydrogen combustion may yield small amounts of nitrogen oxides, along with the water vapour.

Infiltration is the process by which water on the ground surface enters the soil. By this process ground water gets recharged.

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.

Fertilizers are composed of three macronutrients, $NPK$ nitrogen, phosphorous and potassium.

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.