How to determine which of the given redox reactions will occur? Which one of these reactions will occur?
  
  
  $$\ce{KMnO4 -&gt; K2O + MnO2 + O2}$$
  $$\ce{KMnO4 + HCl -&gt; KCl + MnCl2 + Cl2 + H2O}$$
  $$\ce{KMnO4 + CO2 \longrightarrow K2CO3 + Mn2O7}$$
  $$\ce{KMnO4 + CO2 -&gt; K2CO3 + MnO2}$$
  $$\ce{KMnO4 + SO2 -&gt; K2SO4 + Mn2O3 + SO3}$$ 
  


And how am I supposed to know which one it is? It's not just this question, I struggle with these types of questions every time. There seem to be a lot of things to take into consideration.

I'm thinking whether it's under 3 or under 4. The oxidation numbers for the reaction 3 don't change at all. But in reaction 4, only the oxidation number of Mn changes (from +7 to +4) and the other oxidation numbers stay the same (if I'm right). So, I think reactions 1, 2 and 5 definitely happen, but I don't know about 3 and 4.
Both 3 and 4 are impossible. $\ce{CO2}$ does not react with the $\ce{KMnO4}$, because $\ce{KMnO4}$ is strongly oxidizing. $\ce{C}$ is in the highest oxidation state and can not be oxidized, hence, it is impossible to react.