Answer: Option (c) is the correct answer.
Step-by-step explanation:
Troposphere is defined as the lowest region of the atmosphere that extends from the surface of Earth to a height of 6 to 10 km, which is the the lower boundary of stratosphere.
In troposhere, the composition of air consists of nitrogen (78%), oxygen (21%), and 1% argon.
Since, all these gases are not chemically combined to each other in the air present in troposhere. Hence, this air is considered as a mixture.
As a mixture is defined as a substance which contains two or more substance physically combined to each other.
Thus, we can conclude that the air in the troposphere is a mixture.