Which of the following is the best definition of a disproportionation reaction?
A reaction in which a compound breaks down into two or more simpler substances upon heating.
A reaction in which two reactants containing the same element in different oxidation states react to form a single product with an intermediate oxidation state.
A reaction in which a more reactive element displaces a less reactive element from a compound in solution.
A reaction in which the same element in a single chemical species is simultaneously oxidised and reduced.