According to the general formulae for electric and magnetic fields for em waves $E_x=E_0 \sin (k z-\omega t)$ and $B_y=B_0 \sin (k z-\omega t)$; what will be the value of $B_0$ if $E_0=6.3 ~V/m$.

$2.1 \times 10^{-8} ~T$

The correct answer is Option (2) → $2.1 \times 10^{-8} ~T$

In any electromagnetic wave

$E_0=C B_0$ (C is speed of light)

$B_0=\frac{E_0}{C_0}$

$B_0=\frac{E_0}{C}=\frac{6.3}{3 \times 10^8}$

$=2.1 \times 10^{-8} ~T$