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?

$A$ wave front is the locus of all the points where the particles of the medium vibrate with the same:

What is the most important point of Huygens' wave theory?

Spherical wavefronts,as shown in the figure,strike a plane mirror. The reflected wavefront will be as shown in:

Explain the reflection of a plane wavefront from a concave mirror.

The figure shows a surface $XY$ separating two transparent media,medium-$1$ and medium-$2$. The lines $ab$ and $cd$ represent wavefronts of a light wave traveling in medium-$1$ and incident on $XY$. The lines $ef$ and $gh$ represent wavefronts of the light wave in medium-$2$ after refraction. The phases of the light wave at $c, d, e$ and $f$ are $\phi_c, \phi_d, \phi_e$ and $\phi_f$ respectively. It is given that $\phi_c \neq \phi_f$.