7084
In the search for room - temperature batteries with high energy densities , rechargeable metal - air ( more precisely metal - oxygen ) batteries are considered as particularly attractive owing to the simplicity of the underlying cell reaction at first glance .
 Chemical: oxygen
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: oxygen