$A$ ray of monochromatic light is incident on the plane surface of separation between two media $X$ and $Y$ with angle of incidence $i$ in medium $X$ and angle of refraction $r$ in medium $Y$. The given graph shows the relation between $\sin i$ and $\sin r$. If $V_X$ and $V_Y$ are the velocities of the ray in media $X$ and $Y$ respectively,then which of the following is true?

• A
  $V_X = \frac{1}{\sqrt{3}} V_Y$
• B
  $V_X = \sqrt{3} V_Y$
• C
  Total internal reflection can happen when the light is incident in medium $X$.
• D
  $v_X = \sqrt{3} v_Y$,where $v_X$ and $v_Y$ are frequencies of the light in medium $X$ and $Y$ respectively.