Please check the definition of hydrosphere.
the earth is called a blue planet. More than 71 per cent of it is covered with water. As hydrosphere consist of water only (in all its forms, i.e. ice, water vapor and running water etc.) it can't be the part of atmosphere.
Atmosphere is the thin blanket of the earth which surround it. And therefore, the hydrosphere can not be a layer of atmosphere...................

Layers of the Atmosphere and their Characteristics

The atmosphere is composed of different layers, each with its own unique characteristics. These layers are defined based on various factors such as temperature, composition, and altitude. The different layers of the atmosphere include:

1. Troposphere:
- The troposphere is the lowest layer of the atmosphere, extending from the Earth's surface up to about 8-15 kilometers.
- It is where weather phenomena occur and where most of the Earth's air mass is concentrated.
- Temperature generally decreases with altitude in the troposphere.

2. Stratosphere:
- The stratosphere lies above the troposphere, extending from about 15 to 50 kilometers above the Earth's surface.
- It contains the ozone layer, which absorbs and filters out the majority of the sun's ultraviolet radiation.
- Temperature generally increases with altitude in the stratosphere due to the absorption of solar radiation by ozone.

3. Mesosphere:
- The mesosphere is located above the stratosphere, extending from about 50 to 85 kilometers above the Earth's surface.
- It is the coldest layer of the atmosphere and temperatures decrease with altitude.
- Meteoroids burn up in this layer, creating visible streaks of light known as meteors.

4. Thermosphere:
- The thermosphere lies above the mesosphere and extends from about 85 kilometers to the outer reaches of the atmosphere.
- It is characterized by extremely high temperatures due to the absorption of intense solar radiation.
- The International Space Station and various satellites orbit within this layer.

5. Exosphere:
- The exosphere is the outermost layer of the atmosphere and merges with the vacuum of space.
- It is composed of extremely low-density gases and extends hundreds of kilometers above the Earth's surface.
- Satellites in geostationary orbit are located within the exosphere.

Explanation of the Correct Answer

The correct answer is option 'A' - Hydrosphere. The hydrosphere refers to all the Earth's water, including oceans, lakes, rivers, groundwater, and even water vapor in the atmosphere. It is not considered a layer of the atmosphere but rather a part of the Earth's overall system. The hydrosphere interacts with the atmosphere through processes such as evaporation, condensation, and precipitation, but it is not one of the layers of the atmosphere itself.

In conclusion, while the hydrosphere is an important part of the Earth's overall system, it is not one of the layers of the atmosphere. The layers of the atmosphere include the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.