The average kinetic energy includes translational kinetic energy and rotational energy, and each degree of freedom corresponds to kT/2. Translation has three degrees of freedom, and then look at the rotational degrees of freedom: monoatomic molecules (0 rotational degrees of freedom), diatomic molecules or linear molecules (2 rotational degrees of freedom), and nonlinear molecules (3 rotational degrees of freedom). NO2 is a linear molecule, so (3+2)KT/2=5kT/2.