ACB is a right angled glass prism of reflective index 1.5. $\overline{)A},\overline{)B}$  and $\overline{)C}$  are ${60}^0$ , ${30}^0$  and ${90}^0$  respectively. A thin layer of a liquid is on the face AB. For a ray of light which is incident normally on AC to be totally reflected at AB, the refractive index of the liquid on AB shall be

• A

  1.5

• B

  1.4

• C

  1.3

• D

  1.2