( -LRB- ( ( ( The ( atomic mass ) ) ( by definition ) ) ( ( ( ( ( is ( ( ( the number ) ( of ( ( protons plus ) neutrons ) ) ) ( in ( ( the nucleus ) ( of ( the atom ) ) ) ) ) ) , ) and ) ( ( the ( atomic number ) ) ( is ( ( the number ) ( of ( protons ( in ( ( the nucleus ) ( of ( the atom ) ) ) ) ) ) ) ) ) ) . ) ) )
(ROOT (S (-LRB- -LRB-) (NP (NP (DT The) (JJ atomic) (NN mass)) (PP (IN by) (NP (NN definition)))) (VP (VBZ is) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NNS protons) (CC plus) (NNS neutrons))) (PP (IN in) (NP (NP (DT the) (NN nucleus)) (PP (IN of) (NP (DT the) (NN atom))))))) (, ,) (CC and) (S (NP (DT the) (JJ atomic) (NN number)) (VP (VBZ is) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS protons)) (PP (IN in) (NP (NP (DT the) (NN nucleus)) (PP (IN of) (NP (DT the) (NN atom)))))))))) (. .)))
(The atomic mass by definition is the number of protons plus  neutrons in the nucleus of the atom, and the atomic number is the number of protons in the nucleus 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))))) (. .)))