It is because of inability of ns^2 electrons of the valence shell to participate in bonding that :
1. \(Sn^{2+}\) is oxidising while \(Pb^{4+}\) is reducing
2. \(Sn^{2+}\) and \(Pb^{2+}\) are both oxidising and reducing
3. \(Sn^{4+}\) is reducing while \(Pb^{4+}\) is oxidising
4. \(Sn^{2+}\) is reducing while \(Pb^{4+}\) is oxidising