Rb2CO3 + 3 Mg → 2 Rb + 3 MgO + C
This is an oxidation-reduction (redox) reaction:
2 RbI + 2 e- → 2 Rb0 (reduction)
CIV + 4 e- → C0 (reduction)
3 Mg0 - 6 e- → 3 MgII (oxidation)
Rb2CO3 is an oxidizing agent, Rb2CO3 is an oxidizing agent, Mg is a reducing agent.