Properties of EM Waves: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Properties of EM Waves. Understanding the underlying formula is key to arriving at the correct answer below:

The direction of propagation of an EM wave is given by $\vec{E} \times \vec{B}$. It is propagating in $+x$ direction (i.e., $\hat{i}$).
Checking option a: $(-\hat{j} + \hat{k}) \times (-\hat{j} - \hat{k}) = \hat{j} \times \hat{k} - \hat{k} \times \hat{j} = \hat{i} - (-\hat{i}) = 2\hat{i}$, which is parallel to $+x$.
Therefore, option a provides a valid combination.