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One measurement , based on the Arrhenius definition of acidity , is pH , which is a measurement of the hydronium ion concentration in a solution , as expressed on a negative logarithmic scale .
 person: Arrhenius
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
 Entities: Arrhenius 
Answer:
 person: Arrhenius