Distance of nth bright fringe from center is given by :
[tex]y = \dfrac{n\lambda D}{d}[/tex]
Here, D is distance between screen and slit.
d is distance between two slits.
Now, wavelength is written as :
[tex]\lambda = \dfrac{yd}{nD}\\\\\lambda = \dfrac{0.005\times 0.25 \times 10^{-3}}{2\times 1.2}\\\\\lambda = 5.208\times 10^{-7} m = 520.8 \ nm[/tex]
Hence, this is the required solution.
