What does a spectrophotometer measure in this experiment?

• A. pH
• B. Volume
• C. Optical Density
• D. Temperature

Answer: (C)

A spectrophotometer measures how much light a sample absorbs at a specific wavelength, reported as optical density (absorbance). It shines light through a cuvette and detects how much is transmitted; the amount that is absorbed increases with the concentration of the colored substance in the solution, following Beer-Lambert behavior under appropriate conditions. This is why it’s the best choice here — it directly reflects the amount of colored material present. It doesn’t measure pH, volume, or temperature, which require different tools (pH meter, pipette/volume measurement tools, and a thermometer, respectively). In this experiment, you’re using absorbance readings to quantify concentration of a dye or reaction product.