(a) Show that the neutral pion cannot be composed solely of any pair of quarks in which one is an up quark (or an anti-up quark) and one is a down quark (or an anti-down quark).
(b) According to quantum theory, the can be thought of as a sum (superposition) of two different pairs of quarks/antiquarks. Each pair would be either both up or both down quarks. What are these two pairs?