When proteins are placed in an acidic solution, they undergo hydrolysis. This is because the acidic solution has a high concentration of H+ ions, which can react with the peptide bonds that hold amino acids together in a protein chain. Hydrolysis is a reaction that breaks down molecules by adding water, and in the case of proteins, it breaks the peptide bonds between the amino acids. This results in the protein chain being broken into smaller peptides or individual amino acids. Therefore, the correct answer is "Hydrolysis."