Which of the following protein measurement methods relies on colorimetric reaction with phenolic compounds to quantify protein content?

The method that uses a colorimetric reaction with phenolic compounds is the Lowry protein assay. It relies on the Folin‑Ciocalteu reagent, which reacts with phenolic and some other amino‑acid side chains in the protein to produce a blue color. The intensity of that color, measured spectrophotometrically, is proportional to the protein concentration. For example, if you add the reagent to a 1 µg/mL protein solution, the resulting blue hue can be quantified at 750 nm to determine the exact amount of protein present. This approach is more sensitive than the Bradford assay but requires careful handling of the reagent.