A photon is emitted in transition from n = 4ton = 1 level in...

Using the relation between energy of photon and wavelength for the transition in the hydrogen atom, we get

$\dfrac{hc}{\lambda} = 13 . 6\left[1{n}_{1}^{2} - \dfrac{1}{{n}_{2}^{2}}\right]$

$⇒ \dfrac{4 \times {10}^{- 15} \times 3 \times {10}^{8}}{\lambda} = 13 . 6\left[1 - \dfrac{1}{16}\right] ⇒ \lambda = \dfrac{12 \times {10}^{- 7} \times 16}{13 . 6 \times 15} = 94 . 1 \times {10}^{- 9} = 94 . 1nm$