Paragraph: The figure shows a surface $X Y$ separating two transparent media, medium-1 and medium-2. The lines $a b$ and $c d$ represent wavefronts of a light wave travelling in medium-1 and incident on $X Y$. The lines ef and $g h$ represent wavefronts of the light wave in medium-2 after refraction.
Question: 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 $\phi_c \neq \phi_f$.

• A

  $\phi_c$ cannot be equal to $\phi_d$
• B

  $\phi_d$ can be equal to $\phi_e$
• Correct answer
  C

  $\left(\phi_d-\phi_f\right)$ is equal to $\left(\phi_c-\phi_e\right)$
• D

  $\left(\phi_d-\phi_c\right)$ is not equal to $\left(\phi_f-\phi_e\right)$

Hence, the correct answer is option: 'C'.