
Given the following passage

"Hydrogen is commonly used in power stations as a coolant in generators due to a number of favorable properties that are a direct result of its light diatomic molecules. These include low density, low viscosity, and the highest specific heat and thermal conductivity of all gases.",

answer the following question. Note that the answer is present within the text.

Question: A column of rising air that is used by birds to gain height is a? 

thermal
