Young's experiment demonstrates that . . . . . .

In a $YDSE$ with two identical slits,when the upper slit is covered with a thin,perfectly transparent sheet of mica,the intensity at the centre of the screen reduces to $75\%$ of the initial value. The second minimum is observed to be above this point and the third maximum below it. Which of the following cannot be a possible value of the phase difference caused by the mica sheet?

In a Young's double-slit experiment,the intensity at a point where the path difference is $\lambda$ is $K$. What will be the intensity at a point where the path difference is $\lambda / 4$?

In a double-slit experiment performed in air,the angular width of a fringe is found to be $0.15^{\circ}$ on a screen placed $80 \ cm$ away. The wavelength of light used is $490 \ nm$. What is the angular width of the fringe if the entire apparatus is immersed in a medium of refractive index $\frac{5}{3}$ (in $^{\circ}$)?

$A$ beam of light consisting of wavelengths $650 \ nm$ and $550 \ nm$ illuminates the Young's double slits with separation of $2 \ mm$ such that the interference fringes are formed on a screen,placed at a distance of $1.2 \ m$ from the slits. The least distance of a point from the central maximum,where the bright fringes due to both the wavelengths coincide,is . . . . . . $\times 10^{-5} \ m$.

In Young's experiment,the separation between the $5^{\text{th}}$ maxima and the $3^{\text{rd}}$ minima is how many times the fringe width?