a monochromatic beam  of light of wave length 6000A⁰ in vacuum enters a medium of refractive index 1.5 in d medium wat is d frequency  

sorry i misread the question earlier

as frequency remains constant irrespective of the medium

velocity = frequency * wavelength

3 * 10⁸ = f * wavelength

wavelength in mtrs = 6000 * 10^-10  = 6 * 10^-7 mtrs

3 * 10⁸ / 6 * 10^-7 = f

f = 1/2 * 10¹⁵

f=5 * 10¹⁴ Hz

this time i'm sure