The is different from other layers of the atmosphere because it doesn't have a mixture of gases; it has layers of single gases.
a. thermosphere
b. stratosphere
c. troposphere
d. mesosphere

Stratosphere is the layer of atmosphere that is different because it doesn't have mixture of gases, it has layers of single gases.

Explanation:

The layer of atmosphere present above the Troposphere is called Stratosphere.  Hence, it is the second layer of the atmosphere.

Stratosphere is also the layer where ozone is formed. The higher layers of the stratosphere are higher where the lower layers, closer to the earth are cooler. The higher layers are warmer due to the absorption of ultraviolet radiation from the sun.

Above the Stratosphere is the Mesosphere. Above Mesosphere, the atmosphere forms the Thermosphere and finally, above thermosphere is the exosphere.

allowed for the prediction of the properties of missing elements.