( ( ( ( mass number ) ( ( The ( total number ) ) ( of ( ( protons and ) neutrons ) ) ) ) ( in ( ( the nucleus ) ( of ( an atom ) ) ) ) ) . )
(ROOT (NP (NP (JJ mass) (NN number)) (NP (NP (DT The) (JJ total) (NN number)) (PP (IN of) (NP (NNS protons) (CC and) (NNS neutrons)))) (PP (IN in) (NP (NP (DT the) (NN nucleus)) (PP (IN of) (NP (DT an) (NN atom))))) (. .)))
mass number The total number of protons and neutrons in the nucleus of an 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))))) (. .)))