If air is taken as a binary solution, the solvent is

We know that the air we are surrounded by is made up of different gases of which the main constituents are Oxygen, Nitrogen, and Argon.

Air contains 78% of nitrogen and 21% of oxygen and almost 1% of Argon and other gases.

Since, Nitrogen is present in more quantity as compared to other gases, it is the solvent.

Hence, option(a) is the answer.