4553
Therefore , when MnO @ SiO ( 2 ) / Pt ( II ) nanospheres were subjected to an oxidation / reduction cycle by repeatedly switching the flowing gas between air and hydrogen , the nanospheres underwent a reversible change between solid and hollow structures , depending on the gas environment .
 Chemical: MnO; Chemical: SiO ( 2 ); Chemical: Pt ( II ); Chemical: hydrogen
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: MnO; Chemical: SiO ( 2 ); Chemical: Pt ( II ); Chemical: hydrogen