( ( ( ( ( ( Both isotopes ) ( have ( six protons ) ) ) , ) but ) ( ( carbon 12 ) ( ( ( has ( six neutrons ) ) , ) ( while ( ( carbon 13 ) ( has seven ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT Both) (NNS isotopes)) (VP (VBP have) (NP (CD six) (NNS protons)))) (, ,) (CC but) (S (NP (NN carbon) (CD 12)) (VP (VBZ has) (NP (CD six) (NNS neutrons)) (, ,) (SBAR (IN while) (S (NP (NN carbon) (CD 13)) (VP (VBZ has) (NP (CD seven))))))) (. .)))
Both isotopes have six protons, but carbon 12 has six neutrons, while carbon 13 has seven.
(ROOT (S (NP (DT All) (NN carbon) (NNS atoms)) (VP (VBP have) (NP (CD six) (NNS protons))) (. .)))