Given, wavelength of light = 589 nm = 589 x 10^-9 m

Mass of electron m_e = 9.1 x 10^-31 kg

Mass of neutron m_n = 1.67 x 10^-27 kg

Planck's constant h = 6.62 x 10^-34 J - s

Kinetic energy of neutron

                           ${\text{KE}}_{\text{n}}=\frac{{\text{h}}^2}{2{\lambda }^2{\text{m}}_{\text{n}}}$

                                 $=\frac{{\left(6\text{.}63\times 10^{-34}\right)}^2}{2\times {\left(589\times 10^{-9}\right)}^2\times 1\text{.}66\times 10^{-27}}$

                                  $=3\text{.}81\times 10^{-28}\text{ J}$.