The fringe width in Young's double-slit experiment can be increased if we decrease

Which of the following is a true statement if,in Young's double-slit experiment,the separation between the slits is gradually increased?

In Young's double slit experiment,if the separation between coherent sources is halved and the distance of the screen from the coherent sources is doubled,then the fringe width becomes:

In an interference pattern,if the ratio of slit widths is $1:9$,find the ratio of maximum to minimum intensity.

Two wavelengths $\lambda_1 = 450 \ nm$ and $\lambda_2 = 650 \ nm$ are used in Young's double slit experiment. The minimum order of fringe produced by $\lambda_2$ which overlaps with a fringe produced by $\lambda_1$ is $n$. The value of $n$ is . . . . . . .

Two identical narrow slits $S_1$ and $S_2$ are illuminated by light of wavelength $\lambda$ from a point source $P$. If,as shown in the diagram,the light is then allowed to fall on a screen,and if $n$ is a positive integer,the condition for destructive interference at $Q$ is that