Question

The Catalytic Activity of Transition Metals and their compounds are ascribed mainly to:
A.Their unfilled d-orbitals
B.Their ability of adopting variable oxidation states
C.Their chemical reactivity
D.Their magnetic behavior

Answer 1

Hint: Transition elements are elements that have partially filled d orbitals. Transition metals show catalytic behavior mainly due to the following reasons:
a)Partially filled d-orbitals
b)Ability to exhibit variable valences
c)Tendency to form complex compounds

Complete Step By Step Solution:
Transition metals form unstable intermediates with their reactants as they have a tendency to exhibit variable valency and form complexes. The unstable intermediate formed during the reaction provides an alternative path having lower activation energy for the reaction. The lowering of activation energy increases the rate of the reaction. Later these unstable intermediates decompose in order to give the final product and the catalyst is regenerated towards the end of the reaction. Transition metal ions can also change their oxidation states and can become more effective so the Catalytic Activity of Transition Metals and their compounds are ascribed mainly to their ability of adopting variable oxidation states.

So, option-(b) is correct.

Additional Information:
Transition Elements: "Transition metal" is described as any element in the d-block of the periodic table \[\]which includes groups \[3\] to \[12\] on the periodic table. In actual practice, the f-block lanthanide and actinide series are also considered transition metals and are called "inner transition metals". The elements of groups \[4-11\] are generally recognized as transition metals, justified by their typical chemistry, i.e. a large range of complex ions in various oxidation states, colored complexes, and catalytic properties either as the element or as ions (or both). SC and Y in group 3 are also generally recognized as transition metals.
There Properties are:
1.All the Transition elements are metals and most of them are hard, strong, and lustrous, have high melting and boiling points, and are good conductors of heat and electricity.
2.Form many useful alloys with one another and with other metallic elements.
3.These elements dissolve in mineral acids, although a few, such as platinum, silver and gold, are called “noble”—that is, are unaffected by simple (non oxidizing) acids.

The transition metals may be subdivided according to the electronic structures of their atoms into three main transition series, called the first, second, and third transition series, and two inner transition series, called the lanthanides and the antinodes.

Note: Study the periodic table, the various types of groups and periods and the type of metals in them. The various properties of transition elements and their variable oxidation state, leads to their effective catalytic behavior. Reason of variable oxidation states and how these are exhibited.