Which son of Eber was so named because in his days the earth was divided?

Answer: Peleg

Two sons were born to Eber: Peleg, because in his days the earth was divided, and his brother Joktan.

“Two sons were born to Eber: One was named Peleg, because in his days the earth was divided, and his brother was named Joktan.”— Genesis 10:25 (BSB)