( ( ( ( The number ) ( of ( ( hydrogen atoms ) ( in ( ( the ( water molecule ) ) ( -LRB- ( ( H ( 2 O ) ) -RRB- ) ) ) ) ) ) ) ( ( is exactly ) ( of ( two thirds ) ) ) ) ( , ( ( the ( other third ) ) ( ( is ( composed ( of ( an ( oxygen atom ) ) ) ) ) . ) ) ) )
(ROOT (S (S (NP (NP (DT The) (NN number)) (PP (IN of) (NP (NP (NN hydrogen) (NNS atoms)) (PP (IN in) (NP (NP (DT the) (NN water) (NN molecule)) (PRN (-LRB- -LRB-) (NP (NNP H) (QP (CD 2) (CD O))) (-RRB- -RRB-))))))) (VP (VBZ is) (ADVP (RB exactly)) (PP (IN of) (NP (CD two) (NNS thirds))))) (, ,) (NP (DT the) (JJ other) (NN third)) (VP (VBZ is) (VP (VBN composed) (PP (IN of) (NP (DT an) (NN oxygen) (NN atom))))) (. .)))
The number of hydrogen atoms in the water molecule (H 2 O) is exactly of two thirds, the other third is composed of an oxygen atom.
(ROOT (S (NP (NP (CD 2) (NN hydrogen)) (, ,) (NP (CD 1) (NN oxygen) (NNS atoms))) (VP (VBP combine) (S (VP (TO to) (VP (VB make) (PRT (RP up)) (NP (NP (DT a) (NN molecule)) (PP (IN of) (NP (NN water)))))))) (. .)))
2 hydrogen, 1 oxygen atoms combine to make up a molecule of water.