Which of the following is an example of a heterogeneous mixture?

• A. Sand and water
• B. Air
• C. Pure copper
• D. Salt dissolved in water

Answer: (A)

Verified step by step guidance

1. Understand the difference between homogeneous and heterogeneous mixtures. A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture has visibly different components or phases.
2. Analyze each option: Air is a homogeneous mixture because its components (mainly nitrogen, oxygen, and other gases) are uniformly mixed.
3. Pure copper is not a mixture; it is a pure substance consisting of only copper atoms.
4. Salt dissolved in water forms a homogeneous mixture (a solution) because the salt ions are evenly distributed throughout the water.
5. Sand and water form a heterogeneous mixture because the sand particles do not dissolve and remain visibly separate from the water.