In a single slit diffraction experiment first minimum for red light (660 nm) coincides with first maximum of some other wavelength l'. The value of l' is

In a single slit diffraction experiment, position of minima is given by  dsinθ=nλSo for first minima of red   sinθ=1×λRdand as first maxima is midway between first and second minima, for wavelength λ',its position will be ⇒sinθ'=3λ'2dAccording to given condition  sinθ=sinθ' ⇒λ'=23λRSo λ'=23×660=440 nm=4400 Å