Question

If the refractive index of water for light going from air to water be 1.33,what will be the refractive index for light going from air to water?

Answer 1

n21=n2/n1=1.33
so n12=n1/n2=1/1.33

Answer 2

it will be 1.33...... because  the revesibility rule governs the above phenomenon .......hope this will help you .....