( ( In ( ( the case ) ( of ( the ( hydrogen atom ) ) ) ) ) ( , ( there ( ( is ( only ( one electron ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (NP (DT the) (NN case)) (PP (IN of) (NP (DT the) (NN hydrogen) (NN atom))))) (, ,) (NP (EX there)) (VP (VBZ is) (NP (RB only) (CD one) (NN electron))) (. .)))
In the case of the hydrogen atom, there is only one electron.
(ROOT (S (NP (EX There)) (VP (VBP are) (NP (NP (CD one) (NNS electrons)) (PP (IN in) (NP (DT the) (NN hydrogen) (NN atom))))) (. .)))