What is molybdenum?

• A. A nonmetal used to improve ductility
• B. A noble gas used in lighting
• C. A rare earth element used in magnets
• D. This transition metal is added to low-alloy steels to increase the strength of the steel at high temperatures

Answer: (D)

Molybdenum is a transition metal that is widely added to steels to boost strength, especially at high temperatures. In low-alloy steels, small amounts of molybdenum improve hardenability and help the material resist softening and creep when exposed to elevated temperatures, keeping the steel stronger for longer in harsh service. This strengthening comes from solid-solution effects and the formation of hard carbides that impede dislocation motion in the metal’s crystal lattice.

This is distinct from the other categories: it is not a nonmetal, not a noble gas, and not a rare earth element. The description that it is a transition metal added to low-alloy steels to increase high-temperature strength best captures its real role in alloys.