Please solve question no.2

Dear Student

R e f r a c t i v e I n d e x = \frac{S p e e d o f l i g h t i n a i r}{S p e e d o f l i g h t i n d i a m o n d} = \frac{3 \times 10^{8} m / s}{125000 \times 10^{3} m / s} R e f r a c t i v e I n d e x = 2.4

Regards