Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number ?

Explanation

Except secandium (which shows an oxidation state of +3), all other first row transition elements show an oxidation state of +2. This is due to loss of two 4s electrons. In the first half, as we move from `Ti^(2+)` to `Mn^(2+)`, the electronic configuration changes from `3d^(2)` to `3d^(5)`, i.e., number of half-filled d-orbitals increases imparting greater and greater stability to +2 state. In the second half, i.e., `Fe^(2+)` to `Zn^(2+)`, the electronic configuration changes from `3d^(6)` to `3d^(10)`, i.e., the number of half-filled orbital decreases. Hence, the stability of +2 state decreases.