I think it's very roughly around 200,000 K! https://en.wikipedia.org/wiki/De_Laval_nozzle#Exhaust_gas_velocity https://en.wikipedia.org/wiki/De_Laval_nozzle#Ex

I think it's very roughly around 200,000 K! https://en.wikipedia.org/wiki/De_Laval_nozzle#Exhaust_gas_velocity https://en.wikipedia.org/wiki/De_Laval_nozzle#Exhaust_gas_ve... (I'm assuming hydrogen at 200,000 K becomes fully dissociated atomic hydrogen radicals, which act as a helium-like, monoatomic ideal gas—γ = 5/3).