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We have also demonstrated a gel - sol / sol - gel transition by switching the redox states of Fe ( 3 + ) / Fe ( 2 + ) ions .
 Chemical: Fe ( 3 + ); Chemical: Fe ( 2 + )
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: Fe ( 3 + ); Chemical: Fe ( 2 + )