calculate the wavelength , frequency nd wavenumber of a light wave whose period is 2.0 x 10^-10

  given : Time Period = 2* 10^-10 

frequency = 1 / time period = 1 / 2 * 10 ^-10 = 0.5 * 10 ¹⁰   Hz 

wkt , c = wavelength * frequency ==> wavelength = c / frequency ( c is speed of light in vacuum ) 

                                                                   wavelength = 3*10⁸ / 0.5 * 10 ¹⁰ = 6 * 10 ^-2 m 

wave number = 1 / wavelength = 1 / 6 *10^-2 = 0.167 * 10 ² m 

hope u got it