Final answer:
Io, Jupiter's moon, is the most volcanically active planet in our solar system because of tidal heating caused by intense gravitational forces from Jupiter.
Step-by-step explanation:
The reason why Io is the most volcanically active planet in our solar system despite being about the same size as our geologically dead Moon is due to tidal heating. Io is located close to Jupiter and experiences intense gravitational forces from the massive planet. These tidal forces cause Io to be pulled into an elongated shape, creating internal friction and heat.
This process leads to the melting of Io's interior and the eruption of numerous volcanoes.