Answer
$33.3^{\circ}$
Work Step by Step
Let the critical angle be $\theta_{c}$.
So, $\theta_{c}=sin^{-1}\frac{n_{2}}{n_{1}}=sin^{-1}\frac{1.33}{2.42}$, by inserting the values of indexes of refraction for diamond and water.
$\theta_{c}=sin^{-1}0.5495=33.3^{\circ}$
