( ( In ( an atom ) ) ( ( ( protons and ) neutrons ) ( ( form ( ( nucleus , ) ( ( the center ) ( of ( an atom ) ) ) ) ) . ) ) )
(ROOT (S (PP (IN In) (NP (DT an) (NN atom))) (NP (NNS protons) (CC and) (NNS neutrons)) (VP (VBP form) (NP (NP (NN nucleus)) (, ,) (NP (NP (DT the) (NN center)) (PP (IN of) (NP (DT an) (NN atom)))))) (. .)))
In an atom protons and neutrons form nucleus, the center of an atom.
(ROOT (S (NP (NP (DT The) (NN atom)) (PP (IN in) (NP (DT a) (NN neutron)))) (VP (VBZ is) (VP (VBN found) (PP (IN in) (NP (DT the) (DT the) (NN nucleus))))) (. .)))