15986
Detailed analysis shows that the total number of protons at bridging ( terminal ) , eta - O ( mu 2 - O ) , sites ranges from 3 ( 1 ) at pH 7 , to 2 ( 0 ) at pH 11 , to 1 ( 0 ) at pH 15 .
 Chemical: O; Chemical: O
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: O, O 
Answer:
 Chemical: O; Chemical: O