Let's analyze the descriptions of each substance to determine which one is a mixture.
1. Substance P: Formed by boiling pure water.
- When pure water is boiled, it changes from liquid to gas (steam). Steam is still composed of only water molecules (\(H_2O\)), and hence it remains a pure substance, not a mixture.
2. Substance Q: Formed by combining three hydrogen atoms to every nitrogen atom.
- This description refers to the formation of ammonia (\(NH_3\)). Ammonia is a compound because it has a fixed ratio of hydrogen to nitrogen atoms. Compounds are not considered mixtures because they are chemically bonded substances with specific proportions.
3. Substance R: Formed by adding \(5 \, g\) of sugar to \(1 \, L\) of water.
- Adding sugar to water creates a sugar solution. A solution is typically homogeneous, meaning it has uniform composition throughout, but it is still considered a mixture because it involves physically combining two substances (sugar and water) without any chemical bonding between them.
4. Substance S: Formed by compressing carbon under high pressure.
- Compressing pure carbon under high pressure leads to different forms of pure carbon, such as diamond or graphite. Both these forms are composed of only carbon atoms, making them pure substances rather than mixtures.
Based on these descriptions, the substance that is most likely to be a mixture is Substance R (the sugar solution formed by adding \(5 \, g\) of sugar to \(1 \, L\) of water).
So, the correct answer is:
R
