Why is the Earth called " blue planet "?

Hint: The Earth is the third planet from the sun and the fifth largest planet in the solar system. There are a total of 8 planets in our solar system, namely, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The Earth is the only planet in the solar system which supports life.

Complete Step by Step Answer: The Earth is a terrestrial planet which is in the shape of an oblate spheroid. The Earth has a powerful magnetic field and the only planet to have one natural satellite.

The Earth's atmosphere is made up of 78 percent nitrogen and 21 percent oxygen and has traces of water, argon, carbon dioxide and other gases.
Oxygen is found nowhere else in the solar system except the Earth and it makes life possible on it. Among all the metals present in the Earth's surface, iron constitutes about 34.6%. This is the reason for which the Earth has a vast magnetic field.

Around three-fourths of the Earth's surface is made up of oceans and water bodies that constitute 70 per cent of the Earth. That is why it is known as the blue planet.
Moreover, the Earth is the only planet which has water bodies. This water absorbs the light from the Sun and reflects it. On reflecting the white light from the Sun the colour of the light changes to blue. Thus, the Earth appears blue from space.

Note: The Neptune is also referred to as blue sometimes due to the ice present in it. While answering this question do mention both the reasons for which the Earth appears blue.