The speed of electromagnetic waves is the same for .......

$A$ 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 $V/m$?

Given below are two statements: one is labelled as Assertion $(A)$ and other is labelled as Reason $(R).$
Assertion $(A):$ Electromagnetic waves carry energy but not momentum.
Reason $(R):$ Mass of a photon is zero.
In the light of the above statements,choose the most appropriate answer from the options given below:

The dielectric constant of a medium is $8$ and its relative permeability is $200$. If an electromagnetic wave of frequency $100 \text{ MHz}$ travels in this medium,then its wavelength is

$A$ point source of electromagnetic radiation has an average power output of $800\,W$. The maximum value of the electric field at a distance of $4.0\,m$ from the source is...$V/m$

The equation that represents the magnetic field of a plane electromagnetic wave which is propagating along the $x$-direction with a wavelength of $10 \,mm$ and a maximum electric field of $60 \,Vm^{-1}$ in the $y$-direction is (where,$c$ is the speed of light):