Wave number: 

It equals the number of waves per centimetre or per unit distance. It is implies as nu bar ( ) and is equal to the reciprocal of the wavelength expressed in metres (m). The unit of   is metre inverse (m ^-1) though cm^-1 is also commonly employed; whereas the wavelength is expressed in the units of cm.

  = 1/ λ

Velocity:

It is defined as the linear distance travelled through the wave in one second. The velocity in metres per second can be acquired through multiplying frequency in second inverse through wavelength in metres.

c = ν (s ^-1) λ

The velocity of EM radiation depends on the medium. It has maximum value in vacuum and equals 3.00 × 10⁸ m s ^-1.