( ( ( The rest ) ( of ( ( the atom ) ( outside ( the nucleus ) ) ) ) ) ( ( ( is mostly ) ( empty space ) ) . ) )
(ROOT (S (NP (NP (DT The) (NN rest)) (PP (IN of) (NP (NP (DT the) (NN atom)) (PP (IN outside) (NP (DT the) (NN nucleus)))))) (VP (VBZ is) (ADVP (RB mostly)) (NP (JJ empty) (NN space))) (. .)))
The rest of the atom outside the nucleus is mostly empty space.
(ROOT (S (NP (DT The) (NN nucleus)) (VP (VBZ is) (VP (VBN comprised) (ADVP (RB primarily)) (PP (IN of) (NP (JJ empty) (NN space))))) (. .)))