Which of the following substances is a solution of gas in liquid?

A true solution is a homogeneous mixture of two or more chemically non–reacting substances whose composition can be varied with certain limits. Vinegar is a solution of acetic acid in water, i.e. in this, both solute (acetic acid) and solvent (water) are liquids. Thus, it is liquid in liquid solution. Salt solution is an example of solid in liquid solution as in it, salt (solid) is dissolved in water (liquid). Soft drink (i.e. CO₂ dissolved in water) is gas in liquid solution as in this, gaseous solute (CO₂) is dissolved in liquid solvent (water). Air is an example of gas in gas solution.