We can use the following equation to solve this problem:
[tex]y=(2n+1)\frac{\lambda D}{d}[/tex]
Where:
D = distance from the slits to the screen
y = Distance between adjacent dark bands
Therefore:
[tex]\lambda=\frac{yd}{(2n+1)D}[/tex]
So, we need to find d which is the distance between the two slits
Answer:
c)
