State what is meant by an exchange particle.

A meson called the pion was detected in cosmic ray reactions in 1947 by Powell and Occhialini. The pion comes in three possible charge states: π⁺ ,π⁻ and π⁰. The Feynman diagram below represents a possible reaction in which a pion participates.

State and explain whether the meson produced is a π⁺ ,π⁻ or  a π⁰.

a particle that mediates/carries/transmits one of the fundamental forces / a particle that is exchanged between two particles when undergoing one of the fundamental interactions / OWTTE;

π⁺;
from conservation of charge at either vertex, the pion must have charge of +1;