In the Young's double slit experiment, the resultant intensity at a point on the screen is $75 \%$ of the maximum intensity of the bright fringe. Then the phase difference between the two interfering rays at that point is :

Question

$$\begin {array} {1 1} (a)\;\frac{\pi}{6} & \quad (b)\;\frac{\pi}{4} \\ (c)\;\frac{\pi}{3} & \quad (d)\;\frac{\pi}{2} \end {array}$$