The refractive index of diamond is 2.42. What is the meaning of this statement?

Define the refractive index of a medium.

The refractive index of water is 4/3 . Find the speed of light in water.

What is the meaning of an elementary reaction?

What is mean free path?

Two identical equiconvex lenses of refractive index 3/2 and focal length 16cm are kept in contact. The space between the lenses is filled with water of refractive indext 4/3 . What is the focal length of the combination?