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

A

$$Sn^{2+} and Pb^{2+}$$ are both oxidising and reducing

B

$$Sn^{4+}$$ is reducing while $$Pb^{4+}$$ is oxidising

C

$$Sn^{2+}$$ is reducing while $$Pb^{4+}$$ is oxidising

D

$$Sn^{2+}$$ is oxidising while $$Pb^{4+}$$ is reducing