Task: Question Answering
Input (English): Question: When the manganese is oxidized in the air at 1000 ºC it is completely transformed into Mn3O4. This is because: 
 Options:  <1> Mn3O4 is the most volatile of all manganese oxides. <2> Mn3O4 can no longer react with oxygen. <3> There are no manganese oxides with a higher oxidation state. <4> Mn3O4 is the most stable of all manganese oxides. <5> Mn3O4 forms a protective layer that stops oxidation of the metal.
Output (English): 4