answer : 1.91 × 10^8 m/s

given, speed of light in water = 2.5 × 10^8 m/s

refractive index of water = 1.3

refraction index of Ruby = 1.7

so, refractive index of Ruby with respect to water = refractive index of Ruby /refractive index of water = 1.7/1.3

we know, refractive index of any medium is inversely proportional to speed of light in that medium.

i.e.,

here, denotes refractive index of medium and v denotes speed of light in that medium.

here,

so, 1.7/1.3 = 2.5 × 10^8/speed of light in ruby

or, 1.3 × 2.5 × 10^8/1.7 = speed of light in ruby

or, speed of light in ruby = 1.91 × 10^8 m/s