The electric field component of a monochromatic radiation is given...

$\dfrac{dE}{dz} = - \dfrac{dB}{dt}$

$\dfrac{dE}{dz} = - 2{E}_{0}Ksin kzcos \omegat = - \dfrac{dB}{dt}$

$dB = + 2{E}_{0}Ksin kzcos \omega tdt$

$B = + 2{E}_{0}Ksin kz ∫ cos \omega tdt$

$= + 2{E}_{0}\dfrac{k}{\omega}sin kzsin \omegat$

$\dfrac{{E}_{0}}{{B}_{0}} = \dfrac{\omega}{k} = C$

$B = \dfrac{2{E}_{0}}{C}sin kzsin \omegat$

Propagation of EM radiation, Electric field oscillation and Magnetic field oscillation are perpendicular to each other.

Since propagation of EM radiation is $x -$axis and electric field oscillation is along $z -$axis, the Magnetic field oscillation is along $y -$axis.