( ( An acid ) ( ( releases ( ( hydrogen ions ) ( in solution ) ) ) . ) )
(ROOT (S (NP (DT An) (NN acid)) (VP (VBZ releases) (NP (NP (NN hydrogen) (NNS ions)) (PP (IN in) (NP (NN solution))))) (. .)))
An acid releases hydrogen ions in solution.
(ROOT (S (NP (NNS Acids)) (VP (VBP release) (NP (NN hydrogen) (NNS ions)) (, ,) (PP (IN by) (NP (NN definition)))) (. .)))
Acids release hydrogen ions, by definition.