Q.Choose correct option.
Which of the following shows most prominent inert pair effect ?
a. C b. Si c. Ge d. Pb

Every element in groups 13, 14 and 15 can show its group oxidation state (+3, +4, +5 respectively, using all valence electrons) or a state two units lower (+1, +2/-4, +3/-3), and down each group this lower state becomes increasingly stable — the inert-pair effect — because the outer ns2 electron pair is progressively less able to take part in bonding, being poorly shielded by filled inner d (and, from period 6, f) subshells. This is why Tl+1 is more stable than Tl+3, why Pb2+ (PbCl2) is more stable than Pb4+ (PbCl4) while the lighter Ge still favours +4 (GeCl4 over GeCl2), and why heavier group-15 members increasingly favour +3 over +5. A consequence is redox behaviour at the two ends of a group: a species …