Biological inportance of ozone layer is

A ray of light travelling in air have wavelength $$\lambda $$, frequency n, velocity v and intensity $$I$$. If this ray enters into water then these parameters are $$\lambda $$', n', v' and $$I$$' respectively. Which relation is correct from following ?

Optical fibre are based on

A disc is placed on a surface of pond which has refractive index 5/3. A source of light is placed 4 m below the surface of liquid. The minimum radius of disc needed so that light is not coming out is,