Question

in which situation can a mixture always be called a solution?
when one of its components is a gas
when there is no solvent in the mixture
when its components are made up of different types of particles
when the mixture is homogeneous

Explanation:

1. Analyze the first option: A mixture with a gas component (e.g., a mixture of gas and solid like dust in air) is not always a solution. Solutions are homogeneous, but a gas - containing mixture can be heterogeneous (like smoke which has gas and solid particles and is not a solution).
2. Analyze the second option: A solution by definition has a solvent (the component in greater amount that dissolves the solute). If there is no solvent, it can't be a solution.
3. Analyze the third option: All mixtures have different types of particles (since a mixture is a combination of two or more substances). But not all mixtures with different particles are solutions (e.g., a heterogeneous mixture like sand and water).
4. Analyze the fourth option: A solution is a homogeneous mixture, meaning its composition is uniform throughout. So if a mixture is homogeneous, it can always be called a solution.

Answer:

D. when the mixture is homogeneous (assuming the options are labeled A to D as per typical multiple - choice, with the last option being D)