Answer:
Rate law = k1 [N2O5]^2
Explanation:
Rate law only cares about reactants and rate law can only be determined experimentally or by using the coefficients of reactants in elementary reactions
If 2A---->B is an elementary reaction... rate law for this is rate=k[A]^2
So if we look at your question...2N2O5---->2N2O4 + 02 (I think you are missing O2 in question because otherwise equation is unbalanced)
Rate law = k1 [N2O5]^2