( However ( , ( ( a gas ) ( ( is ( ( a substance ) ( ( with neither ) ( ( ( a ( definite shape ) ) nor ) volume ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB However)) (, ,) (NP (DT a) (NN gas)) (VP (VBZ is) (NP (NP (DT a) (NN substance)) (PP (IN with) (ADVP (DT neither)) (NP (NP (DT a) (JJ definite) (NN shape)) (CC nor) (NP (NN volume)))))) (. .)))
However, a gas is a substance with neither a definite shape nor volume.
(ROOT (S (NP (NNP Gas)) (VP (VBZ has) (NP (NP (DT no) (JJ definite) (NN volume)) (CC and) (NP (DT no) (JJ definite) (NN shape)))) (. .)))
Gas has no definite volume and no definite shape.