The electronegativity decreases down the group. C,Ge and Pb all belong to 14 th group. So, the order should be C>Ge>Pb . But the actual order is C>Pb>Ge . This can be explained on the basis of shielding effect. The valence shell electronic configuration of Ge is [Ar] 3d104s24p2 and that of Pb is [Xe] 6s24f145d106p2 . Due to the poor shielding effect of intervening ' f ' electrons in Pb, the Z‌eff ‌ gets highly increased in Pb. Therefore, the electronegativity of Pb is higher than Ge.