( ( ( The nucleus ) ( of ( an atom ) ) ) ( ( is ( composed ( of ( ( ( ( protons and ) neutrons ) , ) ( which ( determine ( ( the mass ) ( of ( the atom ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN nucleus)) (PP (IN of) (NP (DT an) (NN atom)))) (VP (VBZ is) (VP (VBN composed) (PP (IN of) (NP (NP (NNS protons) (CC and) (NNS neutrons)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP determine) (NP (NP (DT the) (NN mass)) (PP (IN of) (NP (DT the) (NN atom))))))))))) (. .)))
The nucleus of an atom is composed of protons and neutrons, which determine the mass of the atom.
(ROOT (S (NP (NP (DT The) (NN mass)) (PP (IN of) (NP (NNS atoms)))) (VP (VBZ is) (VP (VBN based) (PP (IN on) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS protons) (CC and) (NNS neutrons))))) (PP (IN in) (NP (NN nucleus))))) (. .)))