When does Snell's law fail?

Light enters from air into diamond,which has a refractive index of $2.42$. Calculate the speed of light in diamond. The speed of light in air is $3.0 \times 10^{8} \text{ m s}^{-1}$.

An object $1 \, cm$ tall is placed at a distance of $15 \, cm$ from a concave mirror of focal length $10 \, cm$. Find the position,size,and nature of the image formed.

What do you understand by the terms
$(i)$ Real image?
$(ii)$ Virtual image?

One half of a convex lens of focal length $10\, cm$ is covered with a black paper. Can such a lens produce an image of a complete object placed at a distance of $30\, cm$ from the lens? Draw a ray diagram to justify your answer.
$A$ $4\, cm$ tall object is placed perpendicular to the principal axis of a convex lens of focal length $20\, cm$. The distance of the object from the lens is $15\, cm$. Find the nature,position and size of the image.

What will be the angle of refraction for a light ray incident normally at the surface (in $^{\circ}$)?