Which of the following areas in Tropical Africa is densely populated?

South-western Nigeria is densely populated in Tropical Africa. Densely populated areas are those with a high concentration of people living in a given area. In Tropical Africa, there are several factors that influence population density, including climate, soil, vegetation, and water resources. South-western Nigeria has a high population density compared to the other regions mentioned. This is due to several reasons, including favorable climate and fertile soil, which are suitable for agriculture. Also, the region is home to several urban centers, including Lagos, which is one of the most populous cities in Africa. The middle belt of West Africa, the Sahel region of West Africa, and the Niger Delta have lower population densities compared to South-western Nigeria. The middle belt of West Africa is characterized by savannah grassland, while the Sahel region of West Africa is characterized by arid and semi-arid climate. The Niger Delta region is dominated by a network of rivers, creeks, and swamps, which make the area difficult to inhabit. Therefore, South-western Nigeria is the most densely populated area in Tropical Africa among the regions mentioned.