A plane electromagnetic wave propagating along y – direction can have the following pair of electric field $\left(\overrightarrow{E}\right)$  and magnetic field $\left(\overrightarrow{B}\right)$  components.

EM wave is propagating in y-direction.  $\overrightarrow{E}$ and  $\overrightarrow{B}$ vectors are perpendicular to direction of propagation of wave. Hence neither of them have a component along y-axis. Both vectors have to be in x-z plane. $E_x,B_{z}or{E}_z,B_x$   is the correct answer.