Answer» - The transition metals (or, elements) exhibit variable oxidation states due to their electronic configuration, (n – 1) d1-10 ns1-2 for the first row.
- They show only positive oxidation states due to loss of electrons from outer 45-orbital and the penultimate 3rf-orbital.
- Loss of one 45 electron forms M+ ion. Loss of two 45 electrons form M2+ion.
- +2 is the common oxidation state of these elements.
- Higher oxidation states are due to loss of 3 d-electrons along with 45 electrons.
- As the number of unpaired electrons increases, the number of oxidation states shown by the element also increases.
- Sc has only one unpaired electron and it shows two oxidation states (+2 and +3)
- Mn with 5 unpaired d electrons show six different oxidation states. They are +2, +3, +4, +5, +6 and + 7. Thus Mn has the highest oxidation state.
- From Fe onwards variable oxidation states decreases as the number of unpaired electron decreases.
- The last element in the series, Zn shows only one oxidation state (+2).
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