Answer : Option 4) [tex] CO_{2}_{(aq)} [/tex]
Explanation : [tex] CO_{2}_{(aq)} [/tex] is the only sample of matter which can be classified as a solution. As the solution can be defined as a liquid mixture which contains a minor component (the solute) that is uniformly distributed within the major component (the solvent).
In this case, the solute is [tex] CO_{2} [/tex] which is dissolved in water which acts as an solvent. Also, it has a subscript which is aq. which means aqueous, is often given to the solution in which the solvent is water.
Therefore, [tex] CO_{2}_{(aq)} [/tex] is the correct answer.
