Answer
See the answer below.
Work Step by Step
$\Delta E=-Rhc(1/n_f^2-1/n_i^2)$
With $Rhc=2.179\times10^{-19}\ J, n_f=2, n_i=5$
$\Delta E=-4.58\times10^{-20}\ J$
Photon with this energy:
$E=h\times\nu$
$\nu=6.91\times10^{13}\ 1/s$
$c=\lambda\times\nu$
$\lambda=4.34\times10^{-6}\ m$
