( It ( ( ( ( ( is ( ( the lightest ) ( of ( all gases ) ) ) ) , ) and ) ( ( combines easily ) ( with ( ( other elements ) ( to ( form compounds ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VP (VBZ is) (NP (NP (DT the) (JJS lightest)) (PP (IN of) (NP (DT all) (NNS gases))))) (, ,) (CC and) (VP (VBZ combines) (ADVP (RB easily)) (PP (IN with) (NP (NP (JJ other) (NNS elements)) (PP (TO to) (NP (NN form) (NNS compounds))))))) (. .)))
It is the lightest of all gases, and combines easily with other elements to form compounds.
(ROOT (S (NP (JJ Reactive) (NNS elements)) (VP (VBP are) (ADJP (JJ able) (S (VP (TO to) (VP (VB combine) (ADVP (RBR more) (RB easily)) (PP (IN with) (NP (JJ other) (NNS elements)))))))) (. .)))