Final answer:
The ground-based lemur with the largest social group is the red-tailed monkey.
Step-by-step explanation:
The ground-based lemur with the largest social group is the red-tailed monkey. Red-tailed monkeys are primates found in Central and East Africa. They live in groups of 8-30 individuals, making them highly social animals. This social structure allows them to communicate and interact with each other, enhancing their chances of survival.