Which of the following mixtures is classified as a solution?

• A. Smoke in air
• B. Salt dissolved in water
• C. Oil and water mixed together
• D. Sand suspended in water

Answer: (B)

Verified step by step guidance

1. Understand the definition of a solution: A solution is a homogeneous mixture where one substance (the solute) is completely dissolved in another (the solvent), resulting in a single phase with uniform composition throughout.
2. Analyze each mixture given: Smoke in air is a heterogeneous mixture (a colloid or suspension) because smoke particles are dispersed but not dissolved; oil and water mixed together form two separate layers due to immiscibility, so it is a heterogeneous mixture; sand suspended in water is a suspension where solid particles are dispersed but not dissolved, making it heterogeneous.
3. Recognize that salt dissolved in water forms a homogeneous mixture because the salt ions dissociate and disperse uniformly at the molecular level in the water, creating a single-phase solution.
4. Conclude that among the options, only salt dissolved in water meets the criteria of a solution due to its uniform composition and single-phase nature.
5. Remember that solutions are characterized by particles at the molecular or ionic level, which do not settle out or scatter light significantly, unlike suspensions or colloids.