What are neutral pi mesons and charged pi mesons ?
Mesons are subatomic particles consisting of various amounts of quarks. As the name tends to imply, they are capable of holding charge or not holding charge. A meson that has no charge would be considered neutral, while a positively charged meson would have a positive charge on it and a negative meson would have a negative charge on it. This is similar to the way charges are assigned to subatomic particles, protons having a positive charge, neutrons having no charge, and electrons having a negative charge. Mesons may range from less massive to more massive in terms of mass. Generally speaking, as the mass increases, the stability of the meson becomes less stable. Less massive mesons are more stable. This follows the general trend seen with elements on the periodic table of elements, the ones that are most stable are the least massive ones. The elements that have massive nuclei are very unstable, sometimes breaking down to form more stable nuclei.