( ( M Mass ) ( ( ( number ( ( The number ) ( of ( nucleons ( -LRB- ( ( ( protons and ) neutrons ) -RRB- ) ) ) ) ) ) ( in ( ( the nucleus ) ( of ( ( an atom ) ( -LRB- ( ( Symbol A ) -RRB- ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP M) (NNP Mass)) (VP (NP (NN number)) (NP (NP (DT The) (NN number)) (PP (IN of) (NP (NP (NNS nucleons)) (PRN (-LRB- -LRB-) (NP (NP (NNS protons)) (CC and) (NP (NNS neutrons))) (-RRB- -RRB-))))) (PP (IN in) (NP (NP (DT the) (NN nucleus)) (PP (IN of) (NP (NP (DT an) (NN atom)) (PRN (-LRB- -LRB-) (NP (NNP Symbol) (NNP A)) (-RRB- -RRB-))))))) (. .)))
M Mass number The number of nucleons (protons and neutrons) in the nucleus of an atom (Symbol A).
(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))))) (. .)))