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

It is because of the inability of ns2 electrons of the valence shell to participate in bonding that
  1. Sn2+ is reducing while Pb4+ is oxidizing.
  2. Sn2+ is oxidizing while Pb4+ is reducing.
  3. Sn2+ and Pb2+ are both oxidizing and reducing.
  4. Sn4+ is reducing while Pb4+ is oxidizing.

Solution

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

Asked in: NEET 2017

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