( ( ( The reason ) ( why ( ( a gas ) ( ( does not ) ( have ( ( ( a ( definite volume ) ) and ) ( a ( definite shape ) ) ) ) ) ) ) ) ( ( is ( because ( ( the ( ( atoms and ) molecules ) ) ( ( spread out ) ( when ( ( ( the amount ) ( of ( space ( between them ) ) ) ) increases ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN reason)) (SBAR (WHADVP (WRB why)) (S (NP (DT a) (NN gas)) (VP (VBZ does) (RB not) (VP (VB have) (NP (NP (DT a) (JJ definite) (NN volume)) (CC and) (NP (DT a) (JJ definite) (NN shape)))))))) (VP (VBZ is) (SBAR (IN because) (S (NP (DT the) (NNS atoms) (CC and) (NNS molecules)) (VP (VBD spread) (PRT (RP out)) (SBAR (WHADVP (WRB when)) (S (NP (NP (DT the) (NN amount)) (PP (IN of) (NP (NP (NN space)) (PP (IN between) (NP (PRP them)))))) (VP (VBZ increases)))))))) (. .)))
The reason why a gas does not have a definite volume and a definite shape is because the atoms and molecules spread out when the amount of space between them increases.
(ROOT (S (NP (NP (DT The) (NN gas) (NN form)) (PP (IN of) (NP (NN matter)))) (VP (VBZ has) (NP (NP (ADVP (DT neither)) (DT a) (JJ definite) (NN shape)) (CC nor) (NP (DT a) (JJ definite) (NN volume)))) (. .)))