Which of the following is/are NOT solution(s)?
carbon dioxide
Carbon dioxide is not a solution because it is not a mixture. It has only particles of CO2, so, it is a compound. A compound is made up of only one kind of particles. For example, water is a compound as it comprises only H2O particles.
Brass, an alloy, is a solid solution of copper and zinc. Air is a gaseous homogeneous mixture containing a lot of gases. Whereas the ocean water is a liquid solution that contains lots of salts.