Which statement best describes how chemical formulas for pure substances differ from those for mixtures?

• A. Pure substances and mixtures both use chemical formulas to show the physical state of their components.
• B. Mixtures have chemical formulas that indicate the ratio of their components, while pure substances do not have chemical formulas.
• C. Both pure substances and mixtures have fixed chemical formulas that represent their exact composition.
• D. Pure substances have fixed chemical formulas representing definite compositions, while mixtures do not have chemical formulas because their composition can vary.

Answer: (D)

Verified step by step guidance

1. Understand the definition of a pure substance: it is a material with a fixed, definite composition and distinct chemical formula representing the exact ratio of atoms in the compound.
2. Recognize that mixtures are combinations of two or more substances where the components retain their individual properties and the composition can vary; therefore, mixtures do not have a fixed chemical formula.
3. Recall that chemical formulas represent the types and numbers of atoms in a molecule or compound, which applies only to pure substances with definite compositions.
4. Note that mixtures are described by the names or formulas of their individual components, but not by a single chemical formula because their proportions are not fixed.
5. Conclude that the key difference is that pure substances have fixed chemical formulas indicating definite composition, whereas mixtures lack such formulas due to variable composition.