( ( Oxygen gas ) ( ( is ( molecular oxygen ) ) -- ) )
(ROOT (S (NP (NN Oxygen) (NN gas)) (VP (VBZ is) (NP (JJ molecular) (NN oxygen))) (: --)))
Oxygen gas is molecular oxygen --
(ROOT (S (NP (NN Oxygen) (NN gas)) (VP (VBZ is) (VP (VBN given) (PRT (RP off)) (PP (IN by) (NP (NNS plants))))) (. .)))