The following table gives the values of refractive indices of a few media :
Use this table to give an example of (i) a medium pair so that light speeds up when it goes from one of these media to another, (ii) a medium pair so that light slows down when it goes from one of these media to another.
(i) Light speeds up when it travels from an optically denser to an optically rarer medium. In other words, from a medium of high refractive index into a medium of low refractive index. Therefore, one such pair is from crown glass into water or from diamond into crown glass.
(ii) Light slows down when it travels from an optically rarer to an optically denser medium. In other words, from a medium of low refractive index into a medium of high refractive index. One such pair is from water into diamond.
Prasanna, you post the question and again u are the one who also posts the answer. I am confused and compelled.
But anyway thanks for your answer.