Which group of elements exists in nature only as uncombined, free elements?

Noble gases exist in nature only as uncombined, free elements due to their complete valence electron shells, which makes them very stable and largely inert. This stability means that they do not readily form compounds with other elements under normal conditions. Examples of noble gases include helium, neon, argon, krypton, xenon, and radon, which can be found in the atmosphere as isolated atoms rather than bonded to other elements.

In contrast, alkaline metals, transition metals, and halogens typically exist in nature as part of compounds rather than as free elements. Alkaline metals, for instance, are highly reactive and usually found in nature combined with other elements, particularly in salts. Transition metals can also be found in various compounds or in complex forms, while halogens, which are also quite reactive, commonly exist as diatomic molecules but not as uncombined elements. Thus, the unique stability of noble gases is what allows them to exist naturally in a free, uncombined state.