( ( ( Nitrogen -- ) ( ( unusable gas ) ( in ( atmosphere 2 ) ) ) ) . )
(ROOT (NP (NP (NNP Nitrogen)) (: --) (NP (NP (JJ unusable) (NN gas)) (PP (IN in) (NP (NN atmosphere) (CD 2)))) (. .)))
Nitrogen--unusable gas in atmosphere 2.
(ROOT (S (NP (NN Nitrogen) (NN gas)) (VP (VBZ comprises) (NP (NP (QP (RB about) (NNS three-fourths))) (PP (IN of) (NP (NP (NN earth) (POS 's)) (NN atmosphere))))) (. .)))