Final answer:
The correct combination of substances that forms a compound is D) Sulfur dioxide and water forming acid rain, where a chemical reaction between sulfur dioxide and water results in the formation of sulfuric acid, a compound.
Step-by-step explanation:
To classify the combination of substances that forms a compound, we look for a substance that is made up of two or more different elements chemically combined in a fixed ratio. Reviewing the options provided:
- A) Salt and water stirred in a glass is a homogeneous mixture (solution), not a compound, because the salt can be physically separated from the water.
- B) Food coloring in frosting is another example of a homogeneous mixture.
- C) A peanut butter and jelly sandwich is a heterogeneous mixture, as it consists of different components that are easily identifiable and not chemically combined.
- D) Sulfur dioxide and water forming acid rain represents the formation of a compound since sulfur dioxide (SO2) chemically reacts with water (H2O) to form sulfuric acid (H2SO4), which is a compound.
Therefore, the correct answer is D) Sulfur dioxide and water forming acid rain.