The 'lungs of the planet' name is given to:

The correct answer is Option (2) → Amazon rain forest

Option (2) Amazon rain forest — Correct. Of the options, only the Amazon rain forest is given this name, because of its huge size. NCERT names it while describing habitat loss, as it is being cleared for soya beans and cattle.

NCERT Extract:
Loss of Biodiversity – “… The Amazon rain forest (it is so huge that it is called the ‘lungs of the planet’) harbouring probably millions of species is being cut and cleared for cultivating soya beans or for conversion to grasslands for raising beef cattle.”