What characterizes transition metals?

Transition metals are characterized by their ability to exhibit multiple oxidation states and are primarily found in groups 3 to 12 of the periodic table. This characteristic arises from the unique electron configurations of transition metals, which involve the d-orbitals. These d-orbitals can participate in bonding and interaction with other elements, allowing these metals to lose different numbers of electrons and form various oxidation states.

This variability in oxidation states leads to a rich chemistry, including the formation of complexes and colored compounds, which are often associated with the presence of d-electrons. For instance, the different colors of transition metal compounds are often a result of d-d electron transitions when light is absorbed, highlighting the distinct electronic properties of these elements.

The other choices do not accurately represent the characteristics of transition metals. Groups 1 and 2 of the periodic table consist of alkali and alkaline earth metals, which are not considered transition metals. The notion of having a single oxidation state does not apply to transition metals, as many can exist in multiple oxidation states. Lastly, transition metals are indeed known for forming colored compounds rather than not forming them, which is a key identifying feature of these elements.