A plane electromagnetic wave of frequency 25MHz  travels in free space along the x-direction . At a particular point in the space and time, if the intensity of electric field $\overrightarrow{E}=6.3\widehat{j}\text{\hspace{0.17em}V}/\text{m}$, the magnetic induction $\overrightarrow{B}$ at this point is
 

1. Given
Wave Frequency  $=25\text{\hspace{0.17em}MHz}$
Intensity of Electric Field $\overline{E}=6.3\widehat{j}\text{\hspace{0.17em}V}/\text{m}$
The magnitude of the magnetic field is given by
$B=\frac{E}{c}=\frac{6.3}{3\times {10}^8}=2.1\times {10}^{-8}\text{\hspace{0.17em}T}.$ 
2. The vector  $\overrightarrow{E}\times \overrightarrow{B}$ should be along  x-direction, and so
$\widehat{j}\times \left(\widehat{A}\right)=\widehat{i},$  indicates that  $\widehat{A}=\widehat{k}$.
Thus,  $\overrightarrow{B}=2.1\times {10}^{-8}\widehat{k}\text{\hspace{0.17em}T}.$
Therefore, the correct answer is (C).