( ( In contrast ) ( , ( ( ( ( ( ( ( the number ) ( of ( neutrons ( in ( atoms ( of ( some elements ) ) ) ) ) ) ) ( can vary ) ) , ) and ) ( ( ( the ( various forms ) ) ( of ( such elements ) ) ) ( are ( called isotopes ) ) ) ) . ) ) )
(ROOT (S (PP (IN In) (NP (NN contrast))) (, ,) (S (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS neutrons)) (PP (IN in) (NP (NP (NNS atoms)) (PP (IN of) (NP (DT some) (NNS elements)))))))) (VP (MD can) (VP (VB vary)))) (, ,) (CC and) (S (NP (NP (DT the) (JJ various) (NNS forms)) (PP (IN of) (NP (JJ such) (NNS elements)))) (VP (VBP are) (VP (VBN called) (NP (NNS isotopes))))) (. .)))
In contrast, the number of neutrons in atoms of some elements can vary, and the various forms of such elements are called isotopes .
(ROOT (S (NP (NP (DT The) (NN number)) (PP (IN of) (NP (NNS neutrons)))) (VP (MD can) (VP (VB vary) (PP (IN between) (NP (NP (NNS atoms)) (PP (IN of) (NP (DT the) (JJ same) (NN element))))))) (. .)))