The group IV elements show tetravalency due to shifting of one electrons of ns to the vacant np orbital. These four orbitals give rise to four sp3 hybrid orbitals. However, Ge,Sn and Pb, have a tendency to form divalent as well as tetravalent ions. As the inert pair effect increases from Ge to Pb, the stability of tetravalent ion decreases and that of divalent ion increases. Thus, Pb++is more stable than Pb4+ and Sn4+ ions is more stable than Sn2+.