( ( Visible light ) ( ( is ( emitted ( when ( ( an electron ) ( ( drops ( from ( a ( higher ( energy level ) ) ) ) ) ( into ( ( the ( second ( energy level ) ) ) ( of ( the ( hydrogen atom ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Visible) (NN light)) (VP (VBZ is) (VP (VBN emitted) (SBAR (WHADVP (WRB when)) (S (NP (DT an) (NN electron)) (VP (VBZ drops) (PP (IN from) (NP (DT a) (JJR higher) (NN energy) (NN level))) (PP (IN into) (NP (NP (DT the) (JJ second) (NN energy) (NN level)) (PP (IN of) (NP (DT the) (NN hydrogen) (NN atom)))))))))) (. .)))
Visible light is emitted when an electron drops from a higher energy level into the second energy level of the hydrogen atom.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NNS electrons)) (VP (VB return) (PP (TO to) (NP (DT a) (JJR lower) (NN energy) (NN level)))))) (, ,) (NP (PRP they)) (VP (VBP emit) (NP (NP (DT the) (JJ excess) (NN energy)) (PP (IN in) (NP (NP (DT the) (NN form)) (PP (IN of) (NP (NN light))))))) (. .)))