An electromagnetic wave in vacuum has the electric and magnetic fields $$\vec{E}$$ and $$\vec{B}$$, which are always perpendicular to each other. The direction of polarization is given by $$\vec{X}$$ and that of wave propagation by $$\vec{k}$$. Then :

Given:

Electric field = $$\vec E$$

Magnetic field = $$\vec B$$

Polarization direction = $$\vec X$$

Propagation direction = $$\vec k$$

So For an electromagnetic wave, the direction of polarization is the direction of the electric field. Therefore,

$$\vec X\parallel\vec E$$

The electric field, magnetic field and direction of propagation are mutually perpendicular. The direction of propagation is given by the cross product of electric and magnetic fields:

$$\vec k\parallel\vec E\times\vec B$$

So, the correct answer is

$$\vec X\parallel\vec E    and  \vec k\parallel\vec E\times\vec B$$