In a simple, charge-free medium, what is the relationship between the electric field E , magnetic field H , and wave vector k of a time-harmonic plane wave?

Correct option is C

​$$\text{In a simple, linear, homogeneous, isotropic, and charge-free medium, a time-harmonic plane electromagnetic wave has the following fundamental properties:} \\[8pt]\bullet \ \text{The wave vector } \mathbf{k} \text{ indicates the direction of propagation.} \\[4pt]\bullet \ \text{The electric field } \mathbf{E} \text{ and magnetic field } \mathbf{H} \text{ are both transverse to the direction of propagation.} \\[4pt]\bullet \ \text{Hence, } \mathbf{E} \perp \mathbf{k} \text{ and } \mathbf{H} \perp \mathbf{k}. \\[4pt]\bullet \ \text{Additionally, } \mathbf{E}, \mathbf{H}, \text{ and } \mathbf{k} \text{ are mutually perpendicular, with } \mathbf{E} \times \mathbf{H} \text{ pointing in the direction of } \mathbf{k} \text{ (right-hand rule).} \\[10pt]\text{Therefore, the correct relationship is that both } \mathbf{E} \text{ and } \mathbf{H} \text{ are perpendicular to } \mathbf{k}.$$​​