Ans:(a), (c) and (d)

Explanation:

Given that, frequency of charged particles oscillates about mean equilibrium position is: $\boxed{\mathrm{\vartheta }={10}^9 \mathrm{Hz}}$

We know that source of producing electromagnetic wave is accelerated changes.

∴ Frequency of electromagnetic wave is equal to frequency of oscillating charge.  $\boxed{\therefore \mathrm{\vartheta }={10}^9 \mathrm{Hz}}$

Wavelength of electromagnetic wave is

null

The frequency 10⁹ Hz falls in the region of radiowaves.