Answer:
B. Ultraviolet.
Explanation:
Io is the fourth smallest moon in the Galilean moons and it is the innermost moon out of the other three moon. It has the highest density as compare to the moon and it has lowest water at its surface.
While it is Jupiter moon it leaves a footprint of magnet over the Jupiter's upper atmosphere. The appearance of this moon look like as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates. So it reflects Ultraviolet radiations.
