Zuck will fold Elon up like a lawn chair. Elon has size to his advantage. Meanwhile, Zuck has age, conditioning, strength, training, training, and training on his side. Unless Zuck walks into a haymaker, it will not even be close. Elon will get choked out or have his appendages turned into a pretzel.

Elon is also trained in brazilian jiujitsu, or so he claims. Since they are both amateurs, the weight class difference will be an important factor. My money is on Elon.