Which phenomena can be explained by the wave nature of light?

The frequency of a light wave with a wavelength of $500 \, \mathring A$ is $....... \, Hz$.

The correct formula for fringe visibility is

For obtaining maximum contrast between the bright and dark fringes in an interference pattern, the intensities of the two light coherent sources should be

In the figure,the intensity of waves arriving at $D$ from two coherent sources $S_1$ and $S_2$ is $2I_0$ each. The wavelength of the wave is $\lambda = 8\,m$. The resultant intensity at $D$ will be:

What is interference and stationary interference?