Which of the following best describes transition elements?

• A. They are in Groups 3-12
• B. They are all gases at room temperature
• C. They form diatomic molecules
• D. They are nonmetals only

Answer: (B)

Transition elements are the metals in the d-block of the periodic table, the central portion where many familiar metals reside. Their defining feature is that electrons fill d orbitals, which gives them a tendency toward multiple oxidation states and a wide variety of compounds with vivid colors and catalytic versatility. This description best captures what transition elements are because it links their position in the periodic table to their metallic behavior and flexible chemistry. They are not all gases at room temperature—most are solids—nor are they defined by forming diatomic molecules, and they are not nonmetals, since they are metals with characteristic metallic properties.