( ( ( ( ( A ( hydrogen atom ) ) , ) ( for example ) ) , ) ( ( has ( ( ( just ( one proton ) ) and ) ( one electron ) ) ) . ) )
(ROOT (S (NP (NP (DT A) (NN hydrogen) (NN atom)) (, ,) (PP (IN for) (NP (NN example))) (, ,)) (VP (VBZ has) (NP (NP (RB just) (CD one) (NN proton)) (CC and) (NP (CD one) (NN electron)))) (. .)))
A hydrogen atom, for example, has just one proton and 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))))) (. .)))