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

Explanation

As refractive index `= ("speed of light in vacuum")/("speed of light in diamond")`,
`2.42 = (3 xx 10^(8) m//s)/v " " v = (3 xx 10^(8))/(2.42) m//s = 1.24 xx 10^(8) m//s`.
This is the speed of light in diamond.