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.

It gains and loses electrons.

Explanation:

There are following types of redox reactions:

a) combination

b) decomposition

c) combustion

d) displacement

e) Disproportionate: In this reaction a reactant molecule undergoes such a change that the same molecule undergoes reduction as well as oxidation.

Example: