21321
The transition between lobed and hexagonal graphene islands was found to be linked to the concentration of the monatomic hydrogen radical , with low concentrations associated with hexagonal islands .
 Chemical: graphene; Chemical: hydrogen
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: graphene, hydrogen 
Answer:
 Chemical: graphene; Chemical: hydrogen