Which of the following substances is NOT a solution?

• A. Brass
• B. Sand and water mixture
• C. Saltwater
• D. Air

Answer: (B)

Verified step by step guidance

1. Understand the definition of a solution: A solution is a homogeneous mixture where the composition is uniform throughout, and the solute particles are dissolved at the molecular or ionic level in the solvent.
2. Analyze each option to determine if it fits the definition of a solution:
3. Brass is an alloy, which is a solid solution of metals (usually copper and zinc), so it is a solution.
4. Saltwater is a liquid solution where salt (solute) is dissolved uniformly in water (solvent), so it is a solution.
5. Air is a homogeneous mixture of gases (mainly nitrogen, oxygen, and other gases) and is considered a gaseous solution.
6. A sand and water mixture is a heterogeneous mixture because sand particles do not dissolve in water and the mixture is not uniform throughout, so it is NOT a solution.