An acid present in proteins is

Among the options given, the acid present in proteins is an amino acid. Proteins are made up of long chains of amino acids linked together, forming a polypeptide chain. Each amino acid has an amine group (-NH2) and a carboxyl group (-COOH). When these groups react with each other, they form a peptide bond, creating a polypeptide chain. Therefore, the acid present in proteins is the carboxyl group of the amino acids, which gives proteins their acidic properties. Other acids listed, such as lactic acid, propanoic acid, palmitic acid, and stearic acid, are not typically found in proteins. Lactic acid is a byproduct of anaerobic respiration in some organisms. Propanoic acid is a naturally occurring acid found in some foods. Palmitic and stearic acids are both saturated fatty acids found in animal fats and some plant oils.