It is because of the inability of ns 2 electrons of the valence shell to participate in bonding that

Step-by-step solution

The inability of ns 2 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 an oxidizing agent. Sn ( II ) is easily oxidized to Sn ( IV ) ∴         Sn ( II )   is reducing agent.