( ( The ( atomic mass ) ) ( ( is ( ( the number ) ( of ( particles ( in ( ( the nucleus ) ( -LRB- ( ( ( protons plus ) neutrons ) -RRB- ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (JJ atomic) (NN mass)) (VP (VBZ is) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS particles)) (PP (IN in) (NP (NP (DT the) (NN nucleus)) (PRN (-LRB- -LRB-) (NP (NP (NNS protons)) (CC plus) (NP (NNS neutrons))) (-RRB- -RRB-)))))))) (. .)))
The atomic mass is the number of particles in the nucleus (protons plus neutrons).
(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))))) (. .)))