( This ( ( ( ( is ( ( the source ) ( of ( ( the ( H + ) ) ( in ( rain water ) ) ) ) ) ) , ) ( for example ) ) . ) )
(ROOT (S (NP (DT This)) (VP (VBZ is) (NP (NP (DT the) (NN source)) (PP (IN of) (NP (NP (DT the) (NNP H) (NNP +)) (PP (IN in) (NP (NN rain) (NN water)))))) (, ,) (PP (IN for) (NP (NN example)))) (. .)))
This is the source of the H+ in rain water, for example.
(ROOT (S (NP (NN Rain)) (VP (VBZ is) (NP (NP (DT an) (NN example)) (PP (IN of) (NP (JJ liquid) (NN water))))) (. .)))