2 Bi(NO3)3 + 18 KOH + 3 SnCl2 → 3 K2SnO3 + 2 Bi + 6 KCl + 6 KNO3 + 9 H2O
This is an oxidation-reduction (redox) reaction:
2 BiIII + 6 e- → 2 Bi0 (reduction)
3 SnII - 6 e- → 3 SnIV (oxidation)
Bi(NO3)3 is an oxidizing agent, SnCl2 is a reducing agent.