8.19: Compare the stability of +2 oxidation state for the elements of the first transition series. 

Step 1:

The oxidation state shown by 3d elements is as follows:

Sc

+3

Ti

+2

+3

+4

V

+2

+3

+4 +5

Cr

+2

+3

+4 +5 +6

Mn

+2

+3

+4 +5

+6

+7

Fe

+2

+3

+4

+6

Co

+2

+3

+4

Ni

+2

+3

+4

Cu

+1

+2

Zn

+2


Step 2:

From the above table, it is evident that the maximum number of oxidation states is shown

by Mn, varying from +2 to +7. The relative stability of the +2 oxidation state increases on moving from top to bottom. This is because on moving from top to bottom, it becomes more and more difficult to remove the third electron from the d-orbital. 

That why Zn shows show +2 oxidation state.