Both are active, but O is more active w.r.t. N due to its high electronegativity[ En(O) = 3.5 & En(N) = 3.0 ]. Hence, N is more stable w.r.t. O
Nitrogen is more stable as it has half filled configuration in half filled configuration there is larege amount of ionisation enthalpy is required to remove an electron based on the ionisation enthalpy concept nitrogen is more stable than oxygen
if you electro negativity in to consideration then EN FOR NITROGEN IS 3
EN FOR OXYGEN IS 2.5 REGARDING THIS ALSO NITROGEN IS MORE STABLE THAN OXYGEN