( ( ( A molecule ) ( of water ) ) ( ( is ( ( ( two ( hydrogen atoms ) ) and ) ( one ( oxygen atom ) ) ) ) . ) )
(ROOT (S (NP (NP (DT A) (NN molecule)) (PP (IN of) (NP (NN water)))) (VP (VBZ is) (NP (NP (CD two) (NN hydrogen) (NNS atoms)) (CC and) (NP (CD one) (NN oxygen) (NN atom)))) (. .)))
A molecule of water is two hydrogen atoms and one 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.