Which one between N2O4 and NO2 is more susceptible to decompose immediately? And why?

I tried to find Keq for N2 + O2 ==> 2NO2 but no luck. You can calculate it.

Look up delta Go in the tables for the formation constant of NO2 (from the above equation. Then
dGo = -RTlnK. Solve for K at 100 C. Call that Kf. Take 1/Kf for the decomposition of NO2.
I found the decomposition of N2O4 ==> 2NO2 at 100 C to be 6.5.
K for N2O4 decomposition is much larger than K for NO2.