What must be true of a disproportionate substance?

It is composed of oxygen.

It is both a reactant and a product.

It has an oxidation number of 0.

It gains and loses electrons.

The correct answer among the options os the third one. The disproportionate substance has an oxidation number of zero. In a disproportionation reaction is one which a single substance is oxidized and as well reduced. An example is:

2NaOH+Cl2-->NaCl+NaCLO+H2O

From a charge of 0 of Cl into - 1 and + 1.