Long-distance radio broadcasting uses which of the following waves?

Pick out the statement which is not true.

$A$ plane electromagnetic wave of frequency $50\, MHz$ travels in free space along the positive $x-$ direction. At a particular point in space and time, $\vec E = 6.3\,\hat j\,V/m$. The corresponding magnetic field $\vec B$ at that point will be:

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:

If the magnetic field in a plane electromagnetic wave is given by $\overrightarrow{B} = 3 \times 10^{-8} \sin (1.6 \times 10^{3} x + 48 \times 10^{10} t) \hat{j} \; T$,then what will be the expression for the electric field?

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