Question

The element that usually does not show variable oxidation states is :
A. V
B. Ti
C. Sc
D. Cu

Answer 1

Hint: Oxidation state means a number which is assigned to an element to represent the number of electrons lost from that element or the number of electrons consumed by the element. Oxidation state can be both positive or negative. Transition elements show more than one oxidation state.

Complete step by step answer:
In case of transition elements due to presence of electrons at d orbitals , which is closer to the outermost shell of the metal. They show variable oxidation state. With increasing the number of electrons of the d orbitals (up to 5 electrons), the numbers of oxidation state increases.
In case of scandium the number of electrons in the 3d and 4s orbital is 1 and 2 respectively. By removing three electrons from its d and s orbital it forms a very stable inert gas configuration. Therefore, after that electron removal there is no such oxidation state is possible.

So, the correct option is Sc.

Note:
Actinides are f-block elements (atomic number 89 to103) with the general electronic configuration of outermost shell is \[\left[ {{\text{Rn}}} \right]{\text{5}}{{\text{f}}^{{\text{1 - 14}}}}{\text{6}}{{\text{d}}^{{\text{0 - 1}}}}{\text{7}}{{\text{s}}^{\text{2}}}\]. Where the last electron enters to 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 shows greater range of oxidation states. But if we consider lanthanides due to the comparatively small size of 4f orbital they have a limited number of oxidation states.