What is the predominant vegetation zone in northern part of africa around the tropic of cancer? what is similar about vegetation zones surrounding the democratic republic of the congo in africa and central part of brazil?

1. What is the predominant vegetation zone in northern part of Africa around the Tropic of Cancer?

The Tropic of Cancer is a parallel located in the Northern Hemisphere, it crosses Africa to the north in all its extension, in the area of ​​the well-known Sahara Desert.

The Sahara desert or Sahara (a name that means in Arab "the Great Desert") is the most extensive warm desert of the world. Its flora and fauna have adapted to extreme weather conditions.

The central Sahara has a very small number of species that have managed to adapt to survival in the desert. Among these plants, we can mention: acacias, palms, succulents, bushes, and different grasses have adapted to the arid conditions, in addition to cactus. All are small in size to concentrate water. Another characteristic of these species is their capacity for regeneration. The leaves can become completely dry and recover.

2.  What is similar about Vegetation zones surrounding the Democratic Republic of the Congo in Africa and central part of Brazil?

Congo and central Brazil are both are tropical regions.

The tropical region´s on the Earth are located between the Tropic of Cancer and the Tropic of Capricorn. The tropical zones are characterized because they have abundant vegetation.

The characteristics:  

idk if you found them already or not but you probably did but the one closer to sea level is raleigh.