The average kinetic energy of the thermal neutrons is of the order of  (Boltzmann's constant $K_B=8 \times 10^{-5}$ eV/Kelvin)

0.03 eV 3 eV 3 KeV 3 MeV

0.03 eV

$ E = kT = 8 \times 10^{-5} \times 300 = 0.03eV$