Q.meaning of the red underlined part.....how does this effects oxidation states?
or too many d electrons [ hence fewer orbitals available in which to share electrons with others]
Copper and zinc shows lower oxidation state only the reason is they are having many d electrons and they almost occupy all the degenerate d orbitals. In copper (d9 configuration) only one d orbital is left out with unpaired electron and in zinc (d10 configuration) all orbitals are occupied. So there is no such higher oxidation state is possible as in the case of Mn which has d5 configuration with five d orbitals having unpaired electrons. So it shares its electron with all d orbitals whereas copper and zinc cann't.