which must be a mixture of substances? 1. solid

4 is the answer

Solids may be a mixture but they may also be a pure substance. example salt

Liquids may be a mixture but they may also be a pure substance. example water.

Gases may be a mixture but they may also be a pure substance. example oxygen.

Solutions are solutes dissolved in solvents; therefore, these MUST be a mixture.

A mixture is a combination of two or more substances that are not chemically bonded together. Based on this definition, all four options could potentially be mixtures. However, a solution is a specific kind of mixture where a solid, liquid, or gas (solvent) dissolves another substance (solute) to form a homogeneous mixture.

To determine which of the options must be a mixture, we can eliminate the possibilities that cannot exist independently as a mixture.

1. Solid: A solid alone cannot be a mixture since it is a single substance with a definite shape and volume. However, a solid can be part of a mixture when it is combined with other substances, such as in a mixture of different powders or a mixture of different metals.

2. Liquid: A liquid can exist as a pure substance or as part of a mixture. For example, water can be a pure substance or can be mixed with other substances like juice or soda.

3. Gas: Similar to liquids, gases can also exist as pure substances or be part of a mixture. Air, for example, is a mixture of different gases such as nitrogen, oxygen, and carbon dioxide.

4. Solution: By definition, a solution is a type of mixture where a solvent dissolves a solute. Solutions can be formed with solids (e.g., sugar dissolved in water), liquids (e.g., alcohol mixed with water), or gases (e.g., carbon dioxide dissolved in soda).

Therefore, the correct answer is 4. solution, as it specifically refers to a type of mixture formed when a solute is dissolved in a solvent.