Final answer:
Molybdate is best used on ferrous metals, which contain iron and exhibit magnetic properties. It is useful because it can inhibit corrosion on these types of metals.
Step-by-step explanation:
Molybdate is a compound containing the molybdate ion, typically used in various chemical applications. When considering its usability, molybdate is more effective on ferrous metals such as iron or its alloys. This is because molybdate ions can effectively inhibit corrosion on these metals. Ferrous metals, like iron, are defined by their iron content, magnetic properties, and are generally known for conducting electricity and heat well. Considering ferrous metals versus non-ferrous metals, the former contains iron and displays magnetism—as can be confirmed with a magnet test, while the latter do not contain iron and usually resist corrosion more effectively. Therefore, molybdate is best used on ferrous metals due to its corrosion-inhibiting qualities.