The velocity of all radio waves in free space is 3 × 10⁸ m/s. The frequency of a radio wave of wavelength 150m is 

Here : Velocity of electromagnetic waves in free space and wavelength $v=3\times {10}^{8}m/s$ and $\lambda =150m$.

The frequency of radio waves is given by =  $\frac{v}{\lambda }=\frac{3\times {10}^8}{150}=2\times {10}^6 \mathrm{Hz} = 2\mathrm{MHz}$