In vacuum,the speed of light depends upon

Identify the correct statements from the following descriptions of various properties of electromagnetic waves.
$A$. In a plane electromagnetic wave,the electric field and magnetic field must be perpendicular to each other,and the direction of propagation of the wave should be along the electric field or magnetic field.
$B$. The energy in an electromagnetic wave is divided equally between the electric and magnetic fields.
$C$. Both the electric field and magnetic field are parallel to each other and perpendicular to the direction of propagation of the wave.
$D$. The electric field,magnetic field,and direction of propagation of the wave must be mutually perpendicular to each other.
$E$. The ratio of the amplitude of the magnetic field $(B_0)$ to the amplitude of the electric field $(E_0)$ is equal to the reciprocal of the speed of light $(1/c)$.
Choose the most appropriate answer from the options given below:

The ratio of the speeds of electromagnetic waves in a vacuum and in a medium with dielectric constant $K=3$ and permeability $\mu=2\mu_{0}$ is (where $\mu_{0}$ is the permeability of vacuum).

An electromagnetic wave of frequency $2 \text{ MHz}$ propagates from vacuum to a non-magnetic medium of relative permittivity $9$. Then its wavelength

The dimensions of $\frac{1}{{\mu _0}{\varepsilon _0}}$ are .......... .

The magnetic field of a plane electromagnetic wave is given by $B = (400 \ \mu T) \sin [ (4.0 \times 10^{15} \ s^{-1}) (t - \frac{x}{c}) ]$. The average energy density corresponding to the electric field is: