A transitional element is the element, which can form one or more stable ions which have incompletely filled d orbital. Taking this definition, zinc cannot be counted as transitional element. But though copper has 3d¹⁰configuration in its ground state, it can form Cu²⁺ ion with electronic configuration of 3d⁹, so it is considered a transitional element.

Zn²⁺has with electronic configuration of 3d¹⁰so, it does not have any unpaired electron, and thus it cannot undergo d-d transition to impart color to its salts. But, the Cu²⁺ (3d9) has one unpaired electron that undergoes d-d transition to impart color to its salt.

In p-block elements, generally, the electrons of the valence shell only take part in bonding, therefore, in general, the cases of variable oxidation states are limited in these elements. However, in d-block elements, not only the valence shell but also the penultimate shells are incomplete, so they take part in bonding. Thus, they show many variable oxidation states than that of p-block elements.

The important characteristics of transition metals are:

(i) All transition elements are metallic in nature, e.g., all are metals.

(ii) These metals exhibit variable oxidation states.

(iii) Transition metal atoms or ions generally form the complexes with neutral, negative and positive ligands.

(iv) Compounds of transition metals are usually coloured.

(v) The compounds of these metals are usually paramagnetic in nature.

(vi) Transition metals and their compounds act as good catalysts, i.e., they...

Transitional metals are hard, malleable, ductile, and good conductors of heat and electricity. Their common types of structures are face-centered cubic, hexagonal close packing, and base-centered cubic. Since they are of similar sizes, one can easily replace the other in a lattice structure. And they are even miscible in a molten state. So, transition metals form alloys.

ii)Transition metals and their compounds show catalytic activities because of Variable or multiple oxidation states, ability to form complexes, they provide large surface area for adsorption.

II)Cr2+ is reducing agent as its configuration changes from d4 to d3, when it is oxidized to Cr3+ .The d3 configuration have a half-filled t2g level which is very stable. On the other hand, the reduction of Mn3+ to Mn2+ results in the half-filled (d5) configuration which has extra stability hence Mn3+ acts as oxidizing agent.

Copper (I) i.e. Cu1+ has electronic configuration of 3d10, which means it does not have any unpaired electron. This it cannot undergo d-d transition which leaves its salts white. Also, due to no unpaired electron, it is repelled by the magnetic field and is said to show diamagnetism.

Copper (II), i.e. Cu2+ has electronic configuration of 3d9, which means, it has one unpaired electron. So, it undergoes d-d transition that imparts colors to its salts. Also, the molecules with unpaired electrons...

Actinides exhibit larger oxidation states than lanthanides, because of the very small energy gap between 5f, 6d and 7s subshells. Thus, the outermost electrons get easily excited to the higher energy levels, giving variable oxidation states.