Solutions

Soda water contains carbon dioxide gas dissolved under pressure in liquid water. Carbon dioxide is the gaseous solute, and water is the liquid solvent. Therefore it is classified as a gas-in-liquid solution. Air is gas in gas, while the other options describe combinations whose solute and solvent states do not match soda water.

Ethanol is a liquid and water is also a liquid at ordinary conditions. They mix uniformly because ethanol and water are miscible, so the mixture forms a liquid solution. When both the solute and solvent are liquids, it is called a liquid-in-liquid solution. The other options require a solid or gas component, which is absent here.

Sugar is a solid at ordinary conditions, and water is a liquid solvent. When sugar dissolves uniformly in water, the result is classified as a solid-in-liquid solution. The classification follows the states of solute and solvent, not the fact that the sugar disappears from sight. The other options use incorrect component states.

Salt is a solid before it dissolves, and water is a liquid solvent. Dissolving does not change the classification of the solute based on its original physical state for this school-level question. Thus salt in water is a solid-in-liquid solution. Liquid-liquid, gas-gas and gas-in-solid descriptions do not fit the two components.

Brass is an alloy mainly made by mixing copper and zinc. Both metals are solids under ordinary conditions, and the components are mixed in the solid state. Hence brass is treated as a solid-in-solid solution. The other choices describe combinations involving liquids or gases and do not fit the physical states of brass components.

Most common alloys are made by combining metals that are solid at ordinary temperature. Their atoms are mixed within a solid metallic structure, so school-level classification treats them as solid-in-solid solutions. Brass and bronze are familiar examples. Gas-gas and gas-liquid choices describe mixtures with gaseous components, not ordinary metallic alloys.

Oxygen exists as a gas, whereas water is a liquid. When oxygen dissolves in water, oxygen is the gaseous solute and water is the liquid solvent. Hence the mixture is a gas-in-liquid solution. This dissolved oxygen supports aquatic organisms, but that biological importance does not change the classification. The other choices have incorrect state combinations.

Air is a uniform mixture of gases, including a large amount of nitrogen and smaller amounts of oxygen and other gases. The components and the medium are gaseous, so air is classified as a gas-in-gas solution. Sugar water and salt water contain solid solutes in liquid water, while brass is a solid alloy and therefore a solid solution.

Brass is an alloy containing solid copper and zinc mixed in a solid metallic structure. Therefore, it is classified as a solid-in-solid solution. Soda water is gas in liquid, air is gas in gas, and fog is liquid droplets in gas. The physical states of both the solute and solvent make brass the only suitable answer.

A solid-in-liquid solution is formed when a solid substance dissolves uniformly in a liquid. In salt water, salt is a solid solute and water is a liquid solvent, so it has the required type. Air is a gas-in-gas solution, hydrogen in palladium is a gas-in-solid solution, and brass is a solid-in-solid alloy.

Carbon dioxide is a gas and water is a liquid. When carbon dioxide dissolves in water, it forms a gas-in-liquid solution, as in carbonated or soda water. Copper in gold is a solid-in-solid mixture, ethanol in water is liquid-in-liquid, and water droplets in air are a liquid-in-gas dispersion rather than the requested example.

Both ethanol and water are liquids under ordinary conditions, and they mix uniformly. Thus ethanol is the liquid solute and water is the liquid solvent, making a liquid-in-liquid solution. Sugar water is solid in liquid, hydrogen in palladium is gas in solid, and air is gas in gas. Therefore option B is the unambiguous answer.

True-solution particles are extremely small and remain uniformly distributed throughout the solvent. They are not normally visible, do not settle on standing, and pass through ordinary filter paper. Large visible particles that settle are characteristic of a suspension. Solute particles may be solid, liquid, or gas, so they are not restricted to the gaseous state.

The usual naming order states the solute first and the solvent second. Here the solute is solid and the solvent is liquid, so the solution is called a solid-in-liquid solution. Salt dissolved in water is a familiar example. The other options either reverse the states or introduce a gas, so they do not match the information given.

Soda water contains carbon dioxide gas dissolved in liquid water. Therefore, carbon dioxide is the gaseous solute and water is the liquid solvent, giving a gas-in-liquid solution. Brass is solid in solid, sugar water is solid in liquid, and air is gas in gas. Only soda water satisfies both conditions in the question.

Solution types are named by considering the physical states of the solute and solvent. If both the solute and the solvent are liquids, the mixture is called a liquid-in-liquid solution. Ethanol mixed with water is a familiar example. The other choices require both solids, both gases, or a solid solute, so they do not describe the condition given.

Air is a common gas-in-gas solution because it contains several gases mixed uniformly, with nitrogen acting as the major gaseous medium. Brass is a solid alloy, soda water is gas in liquid, and salt water is solid in liquid. Thus only air has both the solute and solvent in the gaseous state.

In salt water, salt is a solid solute and water is a liquid solvent. Therefore, it is a solid-in-liquid solution. Oxygen in water is gas in liquid, ethanol in water is liquid in liquid, and nitrogen in oxygen is gas in gas. Checking the physical state of each named substance makes option B unambiguous.

Ethanol and water are both liquids, so ethanol can act as the liquid solute and water as the liquid solvent. They form a liquid-in-liquid solution. Salt is a solid solute in liquid water, carbon dioxide is a gaseous solute in liquid water, and copper in gold involves solid components. Hence option A is the only correct choice.

Copper and gold are both solids at ordinary conditions. When one metal is uniformly mixed into another solid metal, the result is classified as a solid-in-solid solution or alloy-like solid mixture. Sugar in water is solid in liquid, oxygen in water is gas in liquid, and fog is liquid droplets in gas. Therefore option A matches both required states.

A solution is a homogeneous mixture in which the solute particles are uniformly distributed through the solvent. It may be solid, liquid or gaseous, and it need not be coloured; for example, salt water is usually colourless. It contains at least two components, not just one substance. Therefore the defining statement is that a solution is homogeneous.

Sugar is a solid at ordinary conditions, and the question explicitly identifies water as the solvent. Water is liquid, so the combination is a solid solute in a liquid solvent. Sugar dissolves uniformly to form a solid-in-liquid solution. The other options would require a liquid or gas solute, or a gaseous solvent, none of which applies here.

Air is a homogeneous mixture of gases such as nitrogen, oxygen, argon and carbon dioxide, so it is treated as a gaseous solution. At room temperature, its solvent or continuous medium is gaseous. Salt water and sugar water have liquid water as the solvent, while brass is a solid alloy; therefore, they are not gaseous solutions.

Brass is an alloy mainly formed by mixing copper and zinc. Since both components are solids and the resulting uniform mixture remains solid at room temperature, brass is classified as a solid solution, or a solid-in-solid solution. Soda water, salt water and an ethanol-water mixture have liquid solvents, so they are liquid solutions.

Salt water is formed when solid salt dissolves uniformly in liquid water. The solvent, water, is liquid at room temperature, and the solution therefore remains liquid. Air is a gaseous solution, brass is a solid alloy treated as a solid solution, and hydrogen in palladium is a solid-in-solid solution. Thus salt water is the only liquid solution listed.