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A) Both i, r are equal to zero, i=r=0. B)  \frac{v_{1}}{v_{2}} = n_{21}. Speed of light in diamond = speed in vacuum/refractive index. V=1.19× 10^{8} .
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       when the ray falls normally on a surface, angle of incidence is 0. 
   since μ₁ Sin i = μ₂ sin r    =>  r is also zero.  The ray goes straight in to the glass medium and emerges out of glass slab at the other surface also at  i = 0 and r = 0. 

           Refractive Index is defined as the ratio of speed of light in vacuum divided by speed of light in the medium.  It is also calculated by the formula: Sin i / Sin r.

             μ = 2.52 = 3 * 10⁸ m /sec / v

               v = 3 * 10⁸ / 2.52 = 1.19 * 10⁸ meters / sec

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