Which of the following quantities changes when the velocity of light in a vacuum changes?

An electromagnetic wave of frequency $5\, GHz$ is travelling in a medium whose relative electric permittivity and relative magnetic permeability both are $2$. Its velocity in this medium is $\times 10^{7}\, m/s$.

$A$ laser beam has intensity $17.7 \times 10^{14} \ W/m^2$. The amplitude of the electric field is
[Use $\epsilon_0 = 8.85 \times 10^{-12} \ C^2 / (N \cdot m^2)$]

For a plane electromagnetic wave,the electric field is given by $\vec{E} = 10 \cos(10^7t + kx) \hat{j} \text{ V/m}$. Where $t$ is in seconds and $x$ is in meters,then: $(i)$ The wavelength of this wave is $188.4 \text{ m}$. $(ii)$ The wave vector of this wave is $0.33 \text{ rad/m}$. $(iii)$ The amplitude of the electric field of this wave is $10 \text{ V/m}$. $(iv)$ This wave is propagating in the positive $X$-direction.

$A$ point light source emits electromagnetic ($E$.$M$.) waves in free space. $A$ detector,placed at a distance of $L \text{ m}$,measures the intensity as $I_o$. The detector is now shifted to another location on the same spherical surface,ensuring the angle between the original location and the new location is $45^{\circ}$. The measured intensity at the new location will be . . . . . . .

$A$ plane electromagnetic wave of frequency $25 \text{ MHz}$ travels in free space along the $X$-direction. At a particular point in space and time, the electric field is $\vec{E} = 6.3 \hat{j} \text{ V m}^{-1}$. What is the magnetic field $\vec{B}$ at that point?