$A$ parallel beam of light strikes a piece of transparent glass having a cross-section as shown in the figure below. The correct shape of the emergent wavefront will be (figures are schematic and not drawn to scale)-

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 $\phi_c \neq \phi_f$.

For light diverging from a point source,

Mark the wrong statement.

The phase difference between any two particles in a given wavefront is . . . . . . rad.

Huygens' principle is applicable to