- Analyze the nature of each process: P is a phase change, Q is a chemical reaction (compound), R is a dissolution (mixture), and S is a physical transformation of an element.
- Identify the definition of a mixture as a physical combination of two or more distinct substances.
- Determine that substance R, being a solution of sugar in water, is the correct classification.
- Conclude that the answer is \(\boxed{R}\).
Explanation
- Analyzing the Nature of Each Substance
To determine which substance is a mixture, we must evaluate the nature of each formation process described:
- Substance P: Boiling pure water is a phase change of a single chemical substance (\(H_2O\)). This process does not create a new chemical combination or mix two different substances; it remains pure water (as vapor).
- Substance Q: Combining three hydrogen atoms with one nitrogen atom forms the chemical compound ammonia (\(NH_3\)). This is a chemical reaction that results in a substance with distinct chemical properties, defined as a compound.
- Substance R: Adding sugar to water is a physical process where sugar molecules are distributed throughout the water solvent. This forms a homogeneous mixture known as a solution, where the substances retain their individual chemical identities and are not chemically bonded.
- Substance S: Compressing carbon is a physical process that may change the crystalline structure of the element, resulting in an allotrope (like diamond), which remains a pure elemental substance.
By definition, a mixture is a material composed of two or more distinct chemical substances that are physically combined but not chemically bonded. Substance R fits this definition perfectly.
- Conclusion
Based on the analysis, substance R is the only one described as a physical combination of two distinct chemical substances (sugar and water) that do not react to form a new chemical compound. Therefore, substance R is a mixture. The final answer is \(\boxed{R}\).
Examples
In everyday life, making a cup of tea is a common example of creating a mixture. When you add sugar to your tea, you are dissolving the sugar crystals into the liquid. Even though the sugar disappears from view, it is still there as a solute within the tea solvent, forming a mixture. Like the substance R in our problem, this process is physical and does not create a new chemical substance, allowing you to separate them through processes like evaporation.