Complex sentence: It has a Sea port named Mongla on its outskirts, 48 km south from Khulna city which is the 2nd seaport (after Chittagong seaport) in Bangladesh.
Split into simpler sentences: It has a Sea port named Mongla on its outskirts, 48 km south from Khulna City. Which is the 2nd seaport (after Chittagong seaport) in Bangladesh.