A ray of light incident normally on the horizontal face of the slab and just fail to emerge from the diagonal face of the prism. If prism angle is ${30}^o$ then refractive index of the prism can be

The correct option is B slightly greater than 2
For the ray to graze on the face AC, i-e, $e={90}^o$

From geometry, ${\theta }_c={30}^o$

Let the refractive index of the prism be $\mu$.

Snell' law, ${\mu }_o\times sin{30}^o=1\times 1$

$⟹{\mu }_o=2$

For total internal to occur, means $\theta >{\theta }_c$

$⟹{\mu }_o<2$