Final answer:
Mixing iron filings with salt does not change the color of the mixture as no chemical reaction occurs; it is a physical change where the mixture retains the color of the individual substances.
Step-by-step explanation:
The question revolves around what happens when you mix iron filings with salt. When these two substances are mixed together, the color does not change; the mixture remains a combination of the colors of the individual components (typically grey for the iron filings and white for the salt). This is because the process is a physical change, meaning that no chemical reaction occurs between iron filings and salt, and therefore, no color change is observed.
For comparison, when mercury(II) oxide is heated, a color change occurs as it decomposes into mercury and oxygen, which is a chemical change. Similarly, when zinc metal reacts with hydrochloric acid, hydrogen gas, and zinc chloride are produced, and lead nitrate mixed with potassium iodide results in the formation of a yellow precipitate, all indicating chemical reactions. In the case of iron filings and salt, no such chemical reaction takes place.