Give the reason why life is …

There are several reasons for this. Atmosphere : Earth has a breathable atmosphere. Oxygen is the gas that is required for the life of most creatures. This is present in Earth's atmosphere and also in water. Oxygen is constantly put into the atmosphere by plants and trees. Earth's atmosphere also contains a small amount of carbon dioxide. This is a poisonous gas which makes up most of the atmosphere of planets like Venus and Mars and makes them unable to support human life. However, its smaller presence on Earth is useful as it helps to moderate the planet's temperature and is absorbed by plants during photosynthesis to produce oxygen. Earth's atmosphere is kept on the planet by its pull of gravity. Mars and Mercury are too small to keep atmosphere. As a result, Mercury has no atmosphere, and Mars' atmosphere is very thin, containing gases which have not managed to escape into space yet. Earth's atmosphere is thick enough to prevent poisonous rays of radiation from getting through it (this is what has happened on Mars). Temperature : Earth has a suitable temperature (amount of heat). Earth is situated from the sun at such a distance, that it receives perfect amount of solar energy from the sun, such that the life can sustain. The temperature is maintained by the moderate amount of carbon dioxide in the planet's atmosphere, which is constantly refreshed whenever there is a volcanic eruption. The temperature on Earth does not go from one extreme to the other either. Mercury can be anything from 200°c below freezing to 375°c above. At 375°c, water would only exist as a gas, and the planet would be completely dry. Venus has a surface temperature of 480°c, which would be much too hot for anybody to live in. Mars, although it can reach 25°c, can be as cold as -140°c, a temperature which would freeze blood and water. The other planets are even colder. Water : Earth has water! Water is believed to be the most important chemical necessary for life. It contains the oxygen needed for life and it allows life-providing molecules to move around easily. Water on Earth can be found anywhere, in its three states. Sunlight and photosynthesis : All planets receive light from the Sun, but no planet uses it as usefully as Earth. Trees and plants on the planet produce oxygen through a process called photosynthesis. Plants need the Sun to grow. Something else which helps the plants to photosynthesise on Earth is the length of time the planet takes to spin once on its axis. Taking just under 24 hours means that each side of the planet receives sunlight regularly. If we look at a planet like Venus, which takes 243 days to spin on its axis, it means that for a large period of time certain parts of the planet are in complete darkness. So even if the planet could support life, it would struggle to do so.

Because the other planets can not have atmosphere, air and water

There are several reasons for this.
Atmosphere :
Earth has a breathable atmosphere. Oxygen is the gas that is required for the life of most creatures. This is present in Earth's atmosphere and also in water. Oxygen is constantly put into the atmosphere by plants and trees. Earth's atmosphere also contains a small amount of carbon dioxide. This is a poisonous gas which makes up most of the atmosphere of planets like Venus and Mars and makes them unable to support human life. However, its smaller presence on Earth is useful as it helps to moderate the planet's temperature and is absorbed by plants during photosynthesis to produce oxygen. Earth's atmosphere is kept on the planet by its pull of gravity. Mars and Mercury are too small to keep atmosphere. As a result, Mercury has no atmosphere, and Mars' atmosphere is very thin, containing gases which have not managed to escape into space yet. Earth's atmosphere is thick enough to prevent poisonous rays of radiation from getting through it (this is what has happened on Mars).

Temperature :
Earth has a suitable temperature (amount of heat). Earth is situated from the sun at such a distance, that it receives perfect amount of solar energy from the sun, such that the life can sustain.
The temperature is maintained by the moderate amount of carbon dioxide in the planet's atmosphere, which is constantly refreshed whenever there is a volcanic eruption. The temperature on Earth does not go from one extreme to the other either. Mercury can be anything from 200°c below freezing to 375°c above. At 375°c, water would only exist as a gas, and the planet would be completely dry. Venus has a surface temperature of 480°c, which would be much too hot for anybody to live in. Mars, although it can reach 25°c, can be as cold as -140°c, a temperature which would freeze blood and water. The other planets are even colder.

Water :
Earth has water! Water is believed to be the most important chemical necessary for life. It contains the oxygen needed for life and it allows life-providing molecules to move around easily. Water on Earth can be found anywhere, in its three states.

Sunlight and photosynthesis :
All planets receive light from the Sun, but no planet uses it as usefully as Earth. Trees and plants on the planet produce oxygen through a process called photosynthesis. Plants need the Sun to grow. Something else which helps the plants to photosynthesise on Earth is the length of time the planet takes to spin once on its axis. Taking just under 24 hours means that each side of the planet receives sunlight regularly. If we look at a planet like Venus, which takes 243 days to spin on its axis, it means that for a large period of time certain parts of the planet are in complete darkness. So even if the planet could support life, it would struggle to do so.