Absolute refractive index of glass, n1=1.5=cv1
Where, c = speed of light in air
v1 = speed of light in glass
Absolute refractive index of diamond, n2=cv2
Where, c = speed of light in air
v2 = speed of light in diamond
Refractive index of diamond with respect to glass is given by, n21=n2n1=1.6
Thus, n2=n21×n1=1.6×1.5=2.4
Therefore, the absolute refractive index of diamond is 2.4.