Which of the following is the best explanation for the observed color change in a chemical reaction?

• A. The temperature of the solution increased, causing the color to change.
• B. A new substance with different electronic transitions was formed.
• C. The pH of the solution remained constant throughout the reaction.
• D. The concentration of the reactants decreased, making the solution appear lighter.

Answer: (B)

Verified step by step guidance

1. Step 1: Understand that color changes in chemical reactions are often due to changes in the electronic structure of molecules or ions involved. This means that when a new substance forms, it can absorb and emit light differently, leading to a visible color change.
2. Step 2: Recognize that temperature changes can affect color, but usually only cause minor shifts (like slight changes in intensity or hue), not the formation of a completely new color. Therefore, temperature increase alone is less likely to explain a distinct color change.
3. Step 3: Consider that pH remaining constant means the chemical environment related to acidity or basicity is stable, so it is unlikely to cause a color change if the pH does not vary.
4. Step 4: Note that a decrease in reactant concentration might make a solution appear lighter or less intense in color, but it does not create a new color; it only affects the intensity of the existing color.
5. Step 5: Conclude that the best explanation for a color change is the formation of a new substance with different electronic transitions, because new substances have different energy levels that absorb and emit light differently, causing the observed color change.