The maximum intensity of fringes in Young's experiment is I. If one of the slit is closed, then the intensity at that place becomes I₀ , which of the following relations is true?

Suppose slit width's are equal so they produces waves of equal intensity say I′, 

Resultant intensity at any point ${\mathrm{I}}_{\mathrm{R}}= 4\mathrm{I}\text{'} {\cos }^2\left(\raisebox{1ex}{$\mathrm{\varphi }$}\!\left/ \!\raisebox{-1ex}{$2$}\right.\right)$, where ϕ is the phase difference between the waves at the point of observation.
For maximum intensity, ϕ  = 0^o  ⇒ I_max​ = 4I′ = I......(i)
If one of slit is closed. Resultant intensity at the same point will be I′ only i.e., I′ = I₀​……..(ii)
Comparing equation (i) and (ii), we get:
I = 4I₀​