 
 <prompt> Wetin dem dey call di substance wey dey regulate and make sure say di temperature of one device no pass safe levels? Given di last question, write one context wey contain di answer. E fit be 1 - 20 sentences. Context: <response>: Hydrogen dey common for power stations as e dey cool generators because of some good properties wey dey come from di light diatomic molecules. Dem include low density, low viscosity, and the highest specific heat and thermal conductivity of all gases. 