The following table gives the refractive indices of a few media:

	1	2	3	4	5
Medium	Water	Crown glass	Rock salt	Ruby	Diamond
Refractive Index	1.33	1.52	1.54	1.71	2.42

Use this table to give an example of:(i) a medium pair so that light speeds up when it goes from one of these medium to another.(ii) a medium pair so that light slows down when it goes from one of these medium to another.

(1) Diamond and water is a medium pair where the light speeds up when it goes from diamond to water. The reason behind this is, light speeds up as it travels from a denser medium to a rarer one, ie., from a medium with a higher refractive index to one with a lower refractive index. 

(2) Crown glass and ruby is a medium pair where the light slows down when it goes from crown glass to ruby. The reason is the same that, light slows down as it travels from a rarer medium to a denser one, i.e., from a medium with a lower refractive index to one with a higher refractive index. 

Note: Different pair can also be taken in both the case. 

For example, Crown glass to water, Ruby to water, can be taken for the (i) case.

Water to diamond, Ruby to crown glass, can be taken for the (ii) case.