Hello Dheeraj,

Here, wavelength of light = 4500 angstroms (Given)

Width of slit = 2 * 10^-4 m (Given)

Required angle = 2 * theta ~ 2 * sin theta [For very small angles theta = sin theta]

Therefore, Required angle = 2 * Wavelength / Width

= (2 * 4500 * 10^-10) / (2 * 10^-4)

= 4500 * 10^-6

= 4.5 * 10^-3 radian (Answer)