Which of the following best describes a characteristic of transition metals?

Transition metals are known for their ability to exhibit multiple oxidation states due to the presence of d electrons in their electron configuration. This characteristic arises from the relatively small energy difference between the d orbitals, allowing these metals to lose different numbers of electrons when they form ions or compounds. For example, iron can exist in oxidation states of +2 and +3, while manganese can vary between +2 and +7 oxidation states. This versatility in oxidation states is a fundamental characteristic of transition metals, influencing their reactivity and the types of compounds they can form.

In contrast, the other options do not accurately represent transition metals. They do not typically have low melting points; many have high melting points. Not all transition metals are soft; in fact, many are hard and brittle. Finally, while some transition metal compounds can be colored and some can be soluble in water, this is not true for all members of the group, making it an inaccurate generalization. Thus, the ability to form multiple oxidation states stands out as a defining feature of transition metals.