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Introduction

Water of Class 7

Water is a chemical compound with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at standard ambient temperature and pressure, but it often co-exists on Earth with its solid state, ice, and gaseous state, steam (water vapor) ,Water covers 71% of the Earth's surface, and is vital for all known forms of life. On Earth, 96.5% of the planet's water is found in seas and oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Only 2.5% of the Earth's water is freshwater.

Water occupies a very large area of the Earth’s surface and is also found underground. It is one of the basic necessities of life needed for various activities such as drinking, bathing, washing, etc. It is also needed for irrigation of crops, industries and for navigation. Most of the water on Earth’s surface is found in seas and oceans which is saline and constitutes about 97%. Fresh water is found frozen in the ice-caps at the poles and on snow-covered mountains.

The underground water and the water in rivers, lakes and ponds are also fresh. It constitutes about 3%. Availability of water is one of the important factors that decide the sustainability of life in a region. It not only decides the number of individuals of each species that are able to survive in a particular area, but it also decides the diversity of life there. However, the temperature and nature of soil are other factors that also matter.

Availability of fresh water varies from place to place. Practically every summer, most places have to face a shortage of water. And in rural areas, water supply systems have not been installed, so, people are forced to spend considerable amounts of time in fetching water from far-away sources. However, many municipal corporations are trying water harvesting techniques to improve the availability of water.

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NCERT solutions for class 7 Science prepared by Physics Wallah will help you to solve your NCERT text book exercise.

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