Final answer:
Venus's retrograde rotation is most likely due to a past collision with a massive celestial body, a common occurrence in the early solar system.
Step-by-step explanation:
The retrograde rotation of Venus is thought to be caused by a past collision with a massive celestial body. This idea is based on evidence that suggests the early solar system experienced many such collisions, leading to significant changes in the bodies that make it up, including reversing the rotation of Venus. Geological activity such as intense volcanic activity, while impactful in shaping a planet's surface, does not have the capacity to alter a planet's rotation in this manner.