Elements of which block of the periodic table shows variable oxidation state?

Explanation

In the case of d-block elements due to the presence of electrons at d orbitals, is closer to the outermost shell of the metal. They show variable oxidation states. With increasing the number of electrons of the d orbitals (up to 5 electrons), the number of oxidation states increases. In the case of d electrons due to a lower effective nuclear charge of attraction, the electrons can be removed to form different oxidation states.Actinides are F-block elements(atomic number 89 to103) with the general electronic configuration of the outermost shell being [Rn]5f1,146d0,17s2. Where the last electron enters the inner 5f-orbital of the actinides. Actinides are also known as rare earth metals. Now according to the Aufbau principle(L+S value), the energy order of the orbitals should be 5f<6d<7s but due to the more diffuse orbitals, their energy becomes more or less the same. As a result, electrons can be excited easily. Due to this reason, actinides show a greater range of oxidation states. But if we consider lanthanides due to their comparatively small size of 4f orbital they have a limited number of oxidation states.