( ( An ion ) ( ( is ( ( an atom ) ( which ( ( ( has lost ) or ) ( gained ( an electron ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT An) (NN ion)) (VP (VBZ is) (NP (NP (DT an) (NN atom)) (SBAR (WHNP (WDT which)) (S (VP (VP (VBZ has) (VP (VBN lost))) (CC or) (VP (VBD gained) (NP (DT an) (NN electron)))))))) (. .)))
An ion is an atom which has lost or gained an electron .
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (DT an) (NN atom)) (VP (VBZ gains) (CC or) (VBZ loses) (NP (DT an) (NN electron))))) (NP (PRP it)) (VP (VBZ becames) (NP (DT a) (PRN (-LRB- -LRB-) (NP (NN n)) (-RRB- -RRB-)) (NN ion))) (. .)))