Final answer:
Jupiter has the largest relative moon, Ganymede, among its four large Galilean moons.
Step-by-step explanation:
The planet that has the largest relative moon is Jupiter. Jupiter has four large moons called the Galilean moons, which are Ganymede, Callisto, Europa, and Io. Among these moons, Ganymede is the largest, making it the moon with the largest size in relation to its parent planet.