Light travels a distance $x$ in time $t_1$ in air and $10x$ in time $t_2$ in another denser medium. What is the critical angle for this medium?

1. A
   ${\sin }^{-1}\left(\frac{t_2}{t_1}\right)$
2. B
   ${\sin }^{-1}\left(\frac{1}{10}\frac{t_2}{t_1}\right)$
3. C
   ${\sin }^{-1}\left(\frac{t_1}{10t_2}\right)$
4. D
   ${\sin }^{-1}\left(\frac{10t_1}{t_2}\right)$