(a) At the beginning of the series, +3 oxidation state is stable but towards the end +2 oxidation state becomes stable
b) The oxidation states of 4d series elements vary from +3 for Y and + 2 to +8 for Ru , Cd for +2.
c) The highest oxidation state of 4d elements are found in their compounds with the higher electronegative elements like O, F and Cl. for example: RuO4
d) Generally in going down a group, a stability of the higher oxidation state increases while that of lower oxidation state decreases.