Solute and solvent

In soda water, carbon dioxide is the gaseous solute and water is the liquid solvent. Thus it is a gas-in-liquid solution. Air is gas-in-gas, brass is solid-in-solid, and chloroform in nitrogen is liquid-in-gas. The important distinction is the state of the dissolved substance versus the dissolving medium.

Chloroform is a liquid, so it can be identified as the liquid solute in this example. Nitrogen is a gas and serves as the gaseous solvent. The mixture is therefore liquid in gas. Salt in water is solid in liquid, hydrogen in palladium is gas in solid, and brass is solid in solid, so none of those satisfies both required states.

The broad type of a solution is generally named from the physical state of its solvent, the continuous medium. Thus a gaseous solution has a gaseous solvent; air is a familiar example. A solid solution has a solid solvent, and a liquid solution has a liquid solvent. Water is not compulsory, because solutions can be non-aqueous and can also be solid or gaseous.

Ethanol is a liquid, so in ethanol-in-water it is the liquid solute; water remains the liquid solvent. Oxygen is a gas, so in oxygen-in-water it is the gaseous solute, while water is again the liquid solvent. Thus the solvents have the same state, but the solutes have different states. The other statements incorrectly describe the components.

Soda water contains carbon dioxide dissolved in water. Carbon dioxide is a gas, so it is the gaseous solute, while water is the liquid solvent. Brass is a solid alloy, air is primarily a mixture of gases, and salt water has solid salt as its solute. Therefore only the statement about soda water correctly identifies the solute state.

Air is a homogeneous mixture of gases. Its major component, nitrogen, is generally treated as the gaseous solvent, while the other gases are solutes. In salt water the solvent is liquid water, brass has a solid metallic solvent, and soda water has liquid water as solvent, so the other statements give wrong states.

Ethanol and water are both liquids, so ethanol in water is a liquid-in-liquid solution. Salt is a solid and water is liquid, so salt in water is solid-in-liquid. Both solutions have liquid water as solvent, but the solute states differ. The other pairs represent gaseous or solid categories instead.

Air is a gas-in-gas solution because its solvent and solutes are gases. Camphor in nitrogen has solid camphor as the solute and gaseous nitrogen as the solvent, so it is solid-in-gas. The other pairs contain liquid or solid solvents and therefore do not provide both requested gaseous-solvent types.

Brass is a solid-in-solid solution because its metallic components are solids. Hydrogen in palladium is gas-in-solid because hydrogen is gaseous and palladium is the solid solvent. Both therefore have solid solvents, while the other options contain gaseous or liquid solvents and cannot provide both requested types.

Ethanol is liquid and water is also liquid, so the two components have the same physical state. Ethanol acts as the solute and water as the solvent, making a liquid-in-liquid solution. Salt is solid, oxygen is gas, and hydrogen is gas while palladium is solid, so the other pairs contain unlike states.

Soda water contains gaseous carbon dioxide as the solute and liquid water as the solvent. Thus its component-state description is gas-in-liquid: the gas is the dissolved substance and the liquid is the medium. Air is gas-in-gas, brass is solid-in-solid, and camphor in nitrogen is solid-in-gas, so only soda water fits.

Camphor is a solid substance, so it is the solid solute in the stated example. Nitrogen is a gas and provides the gaseous solvent or medium. Thus the combination is solid in gas. Hydrogen in palladium has a gaseous solute and solid solvent; oxygen in water has gas in liquid; and ethanol in water has liquid in liquid, so those options do not fit.

Hydrogen is gaseous and palladium is a solid metal that can act as the solvent in this standard example. Hence hydrogen in palladium is a gas-in-solid solution. Camphor in nitrogen is solid-in-gas, air is gas-in-gas, and salt water is solid-in-liquid, so none of the distractors has the required pair of states.

Ethanol is a liquid and water is also a liquid. When ethanol mixes uniformly with water, ethanol is treated as the liquid solute and water as the liquid solvent, making a liquid-in-liquid solution. In soda water the solute is gaseous carbon dioxide, brass is a solid alloy, and air is a gaseous mixture. Therefore only ethanol in water has two liquid components in these roles.