Answer and Explanation:
Ideally, researchers would measure the stoichiometry of the mixture labeled with 14C-lactose and a protein. By measuring this stoichiometry, researchers should be able to find a concentration between lactose and protein of 1:1. This concentration is able to determine that the protein has specifically bound to lactose.
In summary, to determine whether the protein binds lactose, researchers need to calculate whether the concentration of these two elements within the mixture is 1:1.