Answer is: D. Tin atoms give electrons to lead(II) ions and are oxidized to tin(II) ions.
Chemical reaction: Sn⁰ + Pb²⁺ → Sn²⁺ + Pb.
Tin atom (oxidation number 0) give two electrons to led ions, oxidation number of tin is greater now (oxidation number +2).
Oxidation is loss of electrons.