Inability of ns2 electrons of the valence shell to participate in bonding on moving down the group in heavier p-block elements is called inert pair effect As a result, Pb(II) is more stable than Pb(IV) Sn(IV) is more stable than Sn(II) ∴Pb(IV) is easily reduced to Pb(II) ∴Pb(IV) is oxidising agent Sn(II) is easily oxidised to Sn(IV) ∴Sn(II) is reducing agent