**Explanation:**

The correct answer is option B, Earth. Earth is known as the Blue Planet because it appears blue when seen from outer space. There are several reasons why Earth is called the Blue Planet:

1. **Abundance of Water:** Earth is the only known planet in our solar system that has large bodies of liquid water on its surface. Water covers about 71% of the Earth's surface, giving it a blue appearance when viewed from space.

2. **The Water Cycle:** Earth has a unique water cycle that involves the continuous movement of water between the atmosphere, land, and oceans. This cycle helps to regulate Earth's temperature and climate. The presence of water in the form of clouds and oceans contributes to the blue color of our planet.

3. **Atmospheric Scattering:** The Earth's atmosphere is composed of molecules that scatter sunlight. Shorter wavelengths of light, such as blue and violet, are scattered more than longer wavelengths, like red and orange. As a result, when sunlight passes through the Earth's atmosphere, the blue light is scattered in all directions, making the planet appear blue.

4. **Reflection from Oceans:** The reflection of sunlight from the surface of the oceans also plays a role in the blue color of Earth. When sunlight hits the surface of the water, it is reflected back and adds to the blue appearance of the planet.

5. **Satellite Images:** The blue appearance of Earth is also evident in satellite images taken from space. These images show the vast expanse of blue oceans and the white clouds that cover the planet.

In conclusion, Earth is known as the Blue Planet because of the abundance of water, the water cycle, atmospheric scattering, reflection from oceans, and the blue appearance seen in satellite images.

The Earth is known as the Blue Planet.