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

In the phenomenon of interference :-
$(a)$ Total energy is conserved
$(b)$ Total energy is not conserved
$(c)$ Only bright fringes are formed
$(d)$ The frequency of two sources is equal

Two coherent sources $S_1$ and $S_2$ are separated by a distance four times the wavelength $\lambda$ of the source. The sources lie along the $y$-axis,whereas a detector moves along the $+x$-axis. Leaving the origin and far-off points,the number of points where maxima are observed is

Two coherent sources of intensity ratio $x^2$ interfere. In the interference pattern,which of the following relations is correct?

The resultant amplitude of the interference of two waves $y_1 = 4 \sin \omega t$ and $y_2 = 3 \sin (\omega t + \frac{\pi}{3})$ is:

The intensities of two coherent sources are $9I$ and $4I$. The intensity at a point where the path difference is $11\lambda$ is: