Question

Which of the following ascribes the catalytic activity of the transition metals and their compounds?
A. Chemical reactivity
B. Magnetic behaviour
C. Unfilled d-orbitals
D. Ability to adopt multiple oxidation states and their complexing ability

Answer 1

Hint- Here, we will proceed by defining transition metals along with their position in the periodic table. Then, we will discuss one of their properties of adopting multiple oxidation states.

Complete answer:
Transition metals are defined as those elements that have (or readily form) partially filled d orbitals. The d-block elements in groups 3–11 are transition elements. The f-block elements, also called inner transition metals (the lanthanides and actinides), also meet this criterion because the d-orbital is partially occupied before the f orbitals. However, the group 12 elements do display some of the same chemical properties and are commonly included in discussions of transition metals.
Transition metals can form compounds with a wide range of oxidation states. As we move from left to right across the first transition series, we see that the number of common oxidation states increases at first to a maximum towards the middle of the periodic table, then decreases.
For the elements scandium through manganese (the first half of the first transition series), the highest oxidation state corresponds to the loss of all of the electrons in both the s and d orbitals of their valence shells. The titanium(IV) ion, for example, is formed when the titanium atom loses its two 3d and two 4s electrons. These highest oxidation states are the most stable forms of scandium, titanium, and vanadium. However, it is not possible to continue to remove all of the valence electrons from metals as we continue through the series. Iron is known to form oxidation states from 2+ to 6+, with iron(II) and iron(III) being the most common. Most of the elements of the first transition series form ions with a charge of 2+ or 3+ that are stable in water, although those of the early members of the series can be readily oxidized by air.
The elements of the second and third transition series generally are more stable in higher oxidation states than are the elements of the first series.
Catalysis at a solid surface involves the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first row transition metals utilise 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening the bonds in the reacting molecules (the activation energy is lowering). Also because the transition metal ions can change their oxidation states, they become more effective as catalysts.
Therefore, the catalytic activity of the transition metals and their compounds is ascribed to their ability to adopt multiple oxidation states and their complexing ability.

Hence, option D is correct.

Note- These transition metals have a large charge by radius ratio. They are hard and have high densities. These metals have high melting and boiling points. They form compounds which are often paramagnetic in nature. They also form coloured ions and compounds. The complexes including transition metals are stable.