Which pairs of species will spontaneously react?
1) 2H⁺ (aq) + 2e⁻ → H₂(s)
2) Sn²⁺ (aq) + 2e⁻ → Sn(s)
3) Cd²⁺ (aq) + 2e⁻ → Cd(s)
4) None of the above