Which of the following do not require a medium for transmission?

What is the range of frequency of $EM$ waves that are reflected back by the ionosphere?

If the relative permeability and dielectric constant of a medium are $\mu_r$ and $K$ respectively,then the refractive index $n$ of the medium is:

$A$ point source of electromagnetic radiation has an average output power of $800 \, W$. What is the maximum value of the electric field at a distance of $3.5 \, m$ from the source in $V/m$?

In an electromagnetic wave,the energy density associated with the magnetic field will be:

On a particular day,the sun delivers an average power of $\left(\frac{6}{\pi} \times 10^3\right) \frac{W}{m^2}$ to the top of Earth's atmosphere. Find the amplitude of the magnetic field for the electromagnetic waves above the atmosphere. (Take $\mu_0 = 4\pi \times 10^{-7} \text{ SI units}$)