If air is taken as a binary solution, the solvent is:
a.) \[{{N}_{2}}\]
b.) \[{{O}_{2}}\]
c.) \[C{{O}_{2}}\]
d.) Ar

Hint: The air we are surrounded by is made up of different elements. It is a mixture of gases like oxygen, nitrogen and other minute amounts of gases.

Complete step by step solution:

Our earth has a layer of gases which is commonly called air. It surrounds our planet forming an atmosphere.
The main constituent of the atmosphere is Oxygen, Nitrogen and Argon. The remaining gases are often called trace gases which are carbon dioxide, methane, nitrous oxide and ozone.
Now let's come back to the question, firstly, let's know what is a solution.
A solution is a type of a homogenous mixture which is composed of two or more substances, in which solute is a substance which is dissolved in another substance which is called solvent.
In a solution, the substance which is present in more quantity is the solvent and the one present in lesser quantity is solute.
Binary solution is a solution of two substances or liquids which are completely miscible with each other. Boiling point of binary solution depends upon the solution composition.
Now if we consider volume, dry air contains 78.08% of nitrogen, 20.95% of Oxygen, 0.93% of Argon, 0.04% carbon and other trace gases.

Since, Nitrogen is present in more quantity as compared to other gases, it is the solvent.
Therefore, the correct answer is option (a).

Note: Atmospheric gases do not react at ordinary temperature, as nitrogen and oxygen are the main constituents it requires a very high temperature for them to react. For example, when lightning takes place many of the nitrogen are converted into oxides and dioxides.