Based on properties of elements in the periodic table, which element is the best conductor of thermal energy?

The best conductor of thermal energy among the elements listed is **D. vanadium (V)**.

Metals, like vanadium, typically have good thermal conductivity due to their free-moving electrons, which facilitate the transfer of thermal energy. In contrast, argon is a noble gas and a poor conductor of heat, germanium is a semiconductor, and polonium, while metallic, does not have superior thermal conductivity compared to vanadium.