When a plane wave front is incident on a concave mirror as shown in the figure,what is the shape of the reflected wave front?

Which of the following generates a plane wavefront?

$A$ light wave is propagating with plane wave fronts of the type $x+y+z=$ constant. The angle made by the direction of wave propagation with the $x$-axis is

The speed of light in water is less than the speed of light in air,confirms the assumption of which theory of light?

An initially parallel cylindrical beam travels in a medium of refractive index $\mu(I) = \mu_0 + \mu_2I$,where $\mu_0$ and $\mu_2$ are positive constants and $I$ is the intensity of the light beam. The intensity of the beam is decreasing with increasing radius. The initial shape of the wavefront of the beam is

$A$ light wave travels in a vacuum along the $x$-axis. Which of the following may represent the wave front?