Zinc in its 2+ oxidation state is an essential metal ion for life. Zn2+ is found bound to many proteins that are involved in biological processes, but unfortunately Zn2+ is also hard to detect by common chemical methods. Therefore, scientists who are interested in studying Zn2+-containing proteins frequently substitute Cd2+ for Zn2+, since Cd2+ is easier to detect. On the basis of the properties of the elements and ions discussed in this chapter, and their positions in the periodic table, describe the pros and cons of using Cd2+ as a Zn2+ substitute. Proteins that catalyze (speed up) chemical reactions are called enzymes. Many enzymes are required for proper metabolic reactions in the body. One problem with using Cd2+ to replace Zn2+ in enzymes is that Cd2+ substitution can decrease, or even eliminate, enzymatic activity. Can you suggest a different metal ion that might replace Zn2+ in enzymes instead of Cd2+?