For an electron in a box, the ground state energy E_1 = 2 ~\text{eV}E 1 =2 eV, For what transition would the energy difference be 5 E_15E 1 (ie. from what starting value of n_in i to what final value of n_fn f )?

lol

explanation:

you'd use the equation that establishes a relationship between  energy  and  wavelength, which looks like this

e=h⋅cλ, where

λ  - the wavelength of the photon; c  - the speed of light, usually given as  3⋅108m/s; h  -  planck's constant, equal to  6.626⋅10−34j s

plug the value you were given for the energy of the photon in the above equation to get the wavelength

e=h⋅cλ⇒λ=h⋅ce

λ=6.626⋅10−34js⋅3⋅108ms−1.257⋅10−24j=1.581⋅10−1m