Given below are two statements: one is labelled as Assertion (A)...

The ratio of the amplitude of the electric field ($E_0$) to the magnetic field ($B_0$) in any medium is equal to the speed of the electromagnetic wave ($v$) in that medium, i.e., $\dfrac{E_0}{B_0} = v$.

When an electromagnetic wave enters a dielectric medium from vacuum, its speed decreases from $c$ to $v = \dfrac{c}{n}$, where $n > 1$ is the refractive index of the medium.

Since the speed $v$ decreases, the ratio $\dfrac{E_0}{B_0}$ also decreases.

Therefore, both Assertion (A) and Reason (R) are true, and Reason (R) correctly explains Assertion (A).

Answer: Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of Assertion (A)