The correct option is C Endothermic
Equilibrium constant 'K' of a reaction changes with temperature.
For endothermic reaction, K increases with increase in temperature. For exothermic reaction, K decreases with increase in temperature.
In the given reaction
at 500 K, K=1×10−10
at 700 K, K=1×10−7
As value of K increases with increase in temperature, so given reaction is an endothermic reaction.