( ( Ionic compounds ) ( ( ( conduct ( electric current ) ) ( when ( they ( are ( molten ( because ( ( the ( constituent ions ) ) ( that ( form ( ( the compound ) ( appear ( when ( ( the ( solid form ) ) ( ( changes phase ) ( into ( the ( liquid one ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Ionic) (NNS compounds)) (VP (VBP conduct) (NP (JJ electric) (NN current)) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (VP (VBP are) (VP (VBN molten) (PP (IN because) (NP (NP (DT the) (JJ constituent) (NNS ions)) (SBAR (WHNP (WDT that)) (S (VP (VBP form) (SBAR (S (NP (DT the) (NN compound)) (VP (VBP appear) (SBAR (WHADVP (WRB when)) (S (NP (DT the) (JJ solid) (NN form)) (VP (VBZ changes) (NP (NN phase)) (PP (IN into) (NP (DT the) (JJ liquid) (NN one))))))))))))))))))) (. .)))
Ionic compounds conduct electric current when they are molten because the constituent ions that form the compound appear when the solid form changes phase into the liquid one.
(ROOT (S (NP (NNP Ionic)) (VP (VBZ compounds) (NP (NP (JJS best) (NN conduct) (NN electricity)) (PP (IN in) (NP (DT a) (JJ liquid) (NN state))))) (. .)))