Answer
The wave is polarized parallel to the z axis.
Work Step by Step
In part (a), we found that the wave travels in the negative direction of the y axis.
According to the equation for the magnetic field component, the $B_x$ shows that the magnetic field oscillates parallel to the x axis.
The direction of an electromagnetic wave is given by: $E \times B$
By the right hand rule, the electric field oscillates parallel to the z axis.
Therefore, the wave is polarized parallel to the z axis.
