Final answer:
The quark structure of a neutral pion consists of a quark-antiquark pair, specifically an up quark and an anti-down quark, with antiparallel spins, resulting in a net electric charge of zero and a total spin of zero.
Step-by-step explanation:
The quark structure of a neutral pion (π0) is that it is composed of a quark-antiquark pair. More specifically, the neutral pion is made up of an up quark (u) and an anti-down quar vice versa, since particles and antiparticles can be interchanged in mesons. This composition allows the neutral pion to have a net electric charge of zero. The quarks in a neutral pion have antiparallel spins, making the total spin of the pion zero, which is consistent with the observed spin-0 property of mesons like the neutral pion. All mesons, such as the pions shown in provided figures, are composed of a quark-antiquark pair. The 'color' of the quarks adds up to white, which means they form a color-neutral combination representing the quark confinement property. Rules for combining quarks suggest that while baryons are made of three quarks, mesons are formations of a quark paired with its corresponding antiquark, leading to the structure of the neutral pion being that of a meson.