( It ( ( is ( equal ( to ( ( the sum ) ( of ( ( the ( relative ( atomic masses ) ) ) ( of ( all ( the ( atoms ( that ( comprise ( a molecule ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (ADJP (JJ equal) (PP (TO to) (NP (NP (DT the) (NN sum)) (PP (IN of) (NP (NP (DT the) (JJ relative) (JJ atomic) (NNS masses)) (PP (IN of) (NP (PDT all) (DT the) (NNS atoms) (SBAR (WHNP (WDT that)) (S (VP (VBP comprise) (NP (DT a) (NN molecule))))))))))))) (. .)))
It is equal to the sum of the relative atomic masses of all the atoms that comprise a molecule.
(ROOT (S (NP (NP (DT The) (NN sum)) (PP (IN of) (NP (NP (DT the) (NNS masses)) (PP (IN of) (NP (NP (DT the) (NNS atoms)) (PP (IN in) (NP (DT the) (NN formula)))))))) (VP (VBZ is) (VP (VBN referred) (PP (TO to) (NP (RB as) (JJ molecular) (NN mass))))) (. .)))