From the following diagram, determine the direction of propagation of an electromagnetic wave.

Inward to the plane of paper

The correct answer is Option (3) → Inward to the plane of paper

$\vec{k} = \vec{E} \times \vec{B}$

$\vec{E}$ is upward, $\vec{B}$ is rightward.

By right-hand rule, $\vec{E} \times \vec{B}$ points into the plane of the paper.

∴ Direction of propagation = Inward to the plane of paper.