Question

why is tropical evergreen forests of Brazil called the lungs of the Earth

Answer 1

The tropical rainforest of Brazil is also known as the Amazon Rainforest and is the biggest rainforest of the world. As it absorbs a large amount of carbon dioxide and produces Oxygen, it is known as the lungs of the Earth.

Answer 2

The tropical evergreen forests of Brazil  are the largest evergreen forest of the world.
So, they convert maximum amount of CO2 to oxygen.This oxygen is useful to all forms of life...

Hence they are called lungs of the Earth