Which of the following examples illustrates the correct application of alkaline copper solution in protein analysis?

Alkaline copper solution is used in protein analysis to precipitate proteins from a mixture before further steps. The correct application is to add the solution to a protein sample, stir gently, and then centrifuge to collect the precipitated proteins. This step removes salts and small molecules, leaving the protein pellet for downstream assays like SDS‑PAGE. For example, after mixing 10 mL of a cell lysate with 1 mL of alkaline copper, you spin it at 12,000 g for 10 minutes, discard the supernatant, and resuspend the pellet in buffer for electrophoresis. This procedure isolates proteins cleanly and is the standard protocol in many biochemistry labs.