Concept:A mixture contains two or more substances combined in any proportion. Mixtures can be homogeneous (uniform composition) or heterogeneous (distinct components visible). Pure substances like compounds are not mixtures.
Explanation:Check each option to see if all items are mixtures.
Option A: Air is a mixture, wood is a mixture, but water is a pure compound. So not all are mixtures.
Option B: Wood and sand are mixtures, but salt (sodium chloride) is a pure ionic compound. So not all are mixtures.
Option C: Sand is a mixture, but salt and water are pure compounds. So not all are mixtures.
Option D: Wood is a heterogeneous mixture, air is a homogeneous mixture, and sand is a heterogeneous mixture. All three are mixtures.
Therefore, only option D contains a set of mixtures.
Answer:D. Wood, Air, Sand