Solutions

Soda water contains carbon dioxide dissolved uniformly in water. Water is the solvent and is liquid, so the overall solution is classified as a liquid solution; it is also an aqueous solution. The presence of a gaseous solute does not make the whole solution gaseous. Air is a gaseous solution and brass is a solid solution, so their classifications in C and D are wrong. Therefore A has both a correct statement and a valid reason.

Air is correctly described as a gaseous solution because its major component, nitrogen, is a gas and acts as the solvent. However, water is not its solvent; air mainly contains a mixture of gases. The other options pair a correct classification with a reason that correctly identifies the solvent state.

A solution is classified according to its components and their physical states. Air is a homogeneous mixture of gases, so it is a gas-in-gas solution; it cannot be described as a solid-in-liquid solution. Thus D is the incorrect pair. Oxygen dissolved in water is gas in liquid, iodine in alcohol is non-aqueous, and brass is a solid solution, so the other three pairs are acceptable.

A reliable method is to identify what is dissolved and what does the dissolving, then determine the physical state of each. The solution type is named from solute state followed by solvent state, while the overall state usually follows the solvent. This method is safer than guessing from colour or memorised examples.

The governing distinction is between dissolution and dispersion. In soda water, carbon dioxide molecules are distributed at the molecular level throughout liquid water, so it is a true gas-in-liquid solution. Fog contains tiny liquid-water droplets dispersed through air; it is an aerosol, not a true solution. Therefore A is correct. B wrongly treats fog as a true solution, C misuses the solvent idea, and D gives the wrong state.

First determine whether the mixture is homogeneous, because a true solution has uniform composition. Next identify which substance is the solute and which is the solvent. Finally note their physical states to classify it as solid, liquid, or gaseous. Colour, smell, container, or memorized names do not establish the solution type reliably.

Hydrogen in palladium can be treated as a binary solution because it contains two components: hydrogen and palladium. Palladium is the solid solvent, so the broad solution category is solid, specifically gas-in-solid. Salt and sugar in water has three components, while air and soda water are not solid solutions.