Physics - EM Waves Question with Solution | TestHub

In an electromagnetic wave, the direction of energy flow is along the direction of the wave propagation. Therefore, the wave propagates along negative z direction. 

Electric field is along the positive y direction and the wave propagates along negative z direction. Thus, magnetic field is in direction perpendicular to both z and y axes. 

Using vector algebra, 

$(-\hat{k})=(+\hat{j})\times \left(\hat{i}\right)$

Hence, magnetic field is in positive $x$ direction.