Comproportionation or symproportionation is a chemical reaction where two reactants, each containing the same element but with a different oxidation number, will form a product in which the elements involved reach the same oxidation number. For example, an element A in the oxidation states 0 and +2 can comproportionate to the state +1. It is opposite to disproportionation, where two or more atoms of the same element originally having the same oxidation state react with other chemical(s) or themselves to give different oxidation numbers.