
Extract the answer to the question from the following context.
Question: Which of the following is not a favorable property of hydrogen: low density, low viscosity, or coolant?
Context: 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.

coolant
