( Carbon-12 ( ( is ( ( ( the isotope ) ( of carbon ) ) ( ( ( whose atomic ) nucleus ) ( contains ( ( ( 6 protons ) and ) ( 6 neutrons ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Carbon-12)) (VP (VBZ is) (NP (NP (DT the) (NN isotope)) (PP (IN of) (NP (NN carbon))) (SBAR (WHNP (WP$ whose) (JJ atomic) (NNS nucleus)) (S (VP (VBZ contains) (NP (NP (CD 6) (NNS protons)) (CC and) (NP (CD 6) (NNS neutrons)))))))) (. .)))
Carbon-12 is the isotope of carbon whose atomic nucleus contains 6 protons and 6 neutrons.
(ROOT (S (NP (NP (DT A) (NN carbon) (NN atom)) (PP (IN with) (NP (NP (CD 6) (NNS protons)) (CC and) (NP (CD 8) (NNS neutrons))))) (VP (VBZ is) (ADVP (RBR more) (RB specifically)) (VP (VBN known) (PP (IN as) (NP (NN carbon) (CD 14))))) (. .)))
A carbon atom with 6 protons and 8 neutrons is more specifically known as carbon 14.