Dark and colour patterns on thin soap films are due to

In a Fresnel's biprism experiment,the fringe width is $1 \,mm$. The distance of the nearest dark fringe from the central bright fringe is .......$mm$.

In a Fresnel biprism experiment,the two positions of the lens give separations between the virtual slits as $16 \; cm$ and $9 \; cm$ respectively. What is the actual distance of separation (in $cm$)?

In a biprism experiment,a wavelength $\lambda$ is used to obtain an interference pattern. The fringe width is $W_1$ at a distance $D_1$ from the screen. When the screen is moved towards the biprism,the fringe width becomes $W_2$ at a distance $D_2$. The distance between the two virtual images of the slit is:

In a biprism experiment,the distance of the second dark fringe from the central fringe is $3 \ mm$. The distance of the sixth bright fringe from the central fringe is (in $mm$)

$A$ circular planar wire loop is dipped in a soap solution and after taking it out,held with its plane vertical in air. Assuming the thickness of the film at the top is very small,as sunlight falls on the soap film,the observer receives reflected light. What does the observer see?