Which of the following chemical zones of atmosphere is located in outer most sphere from earth surface?

Correct option is D

The correct answer is: (d), Both b and c
Helium layer
In the Earth's atmosphere, helium is present in very small concentrations compared to other gases like nitrogen and oxygen. It is a lighter-than-air gas and tends to rise to the upper layers of the atmosphere due to its low molecular weight.
However, helium is not found in a distinct layer within the Earth's atmosphere. Instead, it is dispersed throughout the atmosphere, albeit in very small amounts.
Hydrogen layer
Hydrogen, being the lightest and simplest element, exists in very low concentrations in Earth's atmosphere. It is mainly found in the uppermost layers of the atmosphere, where lighter gases tend to accumulate due to their low molecular weight and the effects of atmospheric escape processes.
However, even in the upper atmosphere, hydrogen concentrations are extremely low compared to other gases. Most of the hydrogen in Earth's atmosphere is thought to be located in the exosphere, which is the outermost layer of the atmosphere
Exosphere is the uppermost layer of the atmosphere extending beyond the ionosphere above a height of about 400 km.
The air is extremely rarefied and the temperature gradually increases through the layer.
Light gases like helium and hydrogen float into the space from here.
Temperature gradually increases through the layer. (As it is exposed to direct sunlight)
This layer coincides with space.

Information booster:
The atmosphere can be divided into five layers according to the diversity of temperature and density. They are:
1. Troposphere Earth’s troposphere extends from Earth’s surface to, on average, about 12 kilometers in height, with its height lower at Earth’s poles and higher at the equator.
2. Stratosphere Located between approximately 12 and 50 kilometers above Earth’s surface, the stratosphere is perhaps best known as home to Earth’s ozone layer.
3. Mesosphere Located between about 50 and 80 kilometers above Earth’s surface, the mesosphere gets progressively colder with altitude. The top of this layer is the coldest place found within the Earth system, with an average temperature of about minus 85 °C (-120 °F).
4. Thermosphere It is located between about 80 and 700 kilometers above Earth’s surface, whose lowest part contains the ionosphere.
Ionosphere It is not a distinct layer as the others mentioned above. Instead, the ionosphere overlaps the mesosphere, thermosphere, and exosphere.
1. Exosphere:
It is located between about 700 and 10,000 kilometers above Earth’s surface, the exosphere is the highest layer of Earth’s atmosphere and, at its top, merges with the solar wind.