What is the estimated total number of species on Earth?

How did ecologists estimate the total number of species on Earth?

Give the correct descending order of organisms with reference to their estimated number found in the Amazon rainforest:
$(a)$ Plants
$(b)$ Invertebrates
$(c)$ Fishes
$(d)$ Mammals
$(e)$ Birds
Choose the correct answer from the options given below:

Choose the incorrect sentence.

The species diversity of animals on earth is (in $;\%$)

Based on the given pie diagram,identify the correct expression with relation to the number of various groups of organisms.