17. Read the following and answer any four questions from 17 (i) to 17 (v).The absolute refractive index of a medium is simply called its refractive index. The ability of a mediumto refract light is also expressed in terms of its optical density. We have been using “rarer mediumand denser medium' which actually means optically rarer medium and optically denser medium. Incomparing two media the one with larger refractive index is optically denser and vice-versa.Material mediumCanada BalsamRefractive indexMaterial mediumAirIceRefractive index1.00031.531.31Water1.33Rock salt1.54Alcohol1.36KeroseneFused quartzCrown glass1.44 Carbon disulphide1.631.46 Dense flint glass1.65Turpentine oil1.47 Ruby1.71Benzene1.50 Sapphire1.771.52 Diamond2.42(1) Name the medium having highest optical density in the following:(a) Water(6) Alcohol(C) Air :(d) Ice(ü) Find the medium with lowest optical density in the following:(a) Benzene(b) Turpentine oil(c) Rock salt(d) Kerose(iii) You are given kerosene, turpentine oil and water. In which of these does the light travel fastest?(a) Kerosene(6) Water© Turpentine oil(d) All of these(iv) In which of the following mediums does the light travel slowest?(6) Water(c) Alcohol(d) Benzene(v) Which of the following statements is correct regarding the propagation of light of different coloursof white light in air?(a) Red light moves fastest.(1) Blue light moves faster than green light.(c) All the colours of the white light move with the same speed.(d) Yellow light moves with the mean speed as that of the red and the violet light.(a) Air©​