Write the formula for fringe width.

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: If Young's double slit experiment is performed in an optically denser medium than air,then the consecutive fringes come closer.
Reason $(R)$: The speed of light reduces in an optically denser medium than air while its frequency does not change.
In the light of the above statements,choose the most appropriate answer from the options given below:

In an interference arrangement similar to Young's double slit experiment,the slits $S_1$ and $S_2$ are illuminated with coherent microwave sources each of frequency $10^6 \ Hz$. The sources are synchronized to have zero phase difference. The slits are separated by distance $d = 150 \ m$. The intensity $I(\theta)$ is measured as a function of $\theta$,where $\theta$ is defined as shown. If $I_0$ is the maximum intensity,then $I(\theta)$ for $0 \le \theta \le 90^\circ$ is given by:

In a Young's double slit experiment with slit separation $0.1\, mm$,one observes a bright fringe at angle $\frac{1}{40}\, rad$ by using light of wavelength $\lambda_1$. When the light of wavelength $\lambda_2$ is used,a bright fringe is seen at the same angle in the same setup. Given that $\lambda_1$ and $\lambda_2$ are in the visible range ($380\, nm$ to $740\, nm$),their values are:

In Young's double-slit experiment,if the separation between the slit and the screen increases,the fringe width:

What happens to the fringe width in Young's double-slit experiment if it is performed in glycerine instead of air?