( Concentration ( ( is ( ( the number ) ( of ( particles ( in ( ( a volume ) ( of space ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Concentration)) (VP (VBZ is) (NP (NP (DT the) (NN number)) (PP (IN of) (NP (NP (NNS particles)) (PP (IN in) (NP (NP (DT a) (NN volume)) (PP (IN of) (NP (NN space))))))))) (. .)))
Concentration is the number of particles in a volume of space.
(ROOT (S (NP (NP (DT The) (NN number)) (PP (IN of) (NP (NP (NNS particles)) (PP (IN of) (NP (NP (DT a) (NN substance)) (PP (IN in) (NP (DT a) (VBN given) (NN volume)))))))) (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (DT the) (NN concentration))))) (. .)))