In a double-slit interference experiment you are asked to use laser light of different wavelengths and determine the separation between adjacent maxima. You observe that this separation is greatest when you illuminate the double slit with

y = m λ L / d

must use lasers of greater wavelength

Explanation:

The expression for the constructive interference of a double slit is

           d sin θ = m λ

let's use trigonometry to find the angle

          tan θ = y / L

in interference phenomena the angles are small

         tan θ= sin θ/ cos θ = sin θ

         sin θ = y / L

we subjugate

         d y / L = m λ

         y = m λ L / d

In this expression we see that the separation of the lines (and) increases linearly with the wavelength, therefore we must use lasers of greater wavelength