In a double slit experiment, when light of wavelength 400 nm was used, the angular width of the first minima formed on a screen placed 1 m away, was…

In a double slit experiment, when light of wavelength $\displaystyle 400$ nm was used, the angular width of the first minima formed on a screen placed $\displaystyle 1$ m away, was found to be $\displaystyle 0.2^{\circ}$. What will be the angular width of the first minima, if the entire experimental apparatus is immersed in water ? $\displaystyle \left(\mu_{\text {water }}=4 / 3\right)$