This is a multiple choice question on plane wave propagation in electromagnetic field as found in the attached file.
Please see attached file
My answer is shown below. Note that for a multiple choice question, if you can choose the correct answer without working out the whole calculation, please do so because it will save you time. In this particular question, you can already choose B after working out the wavelength (without even knowing the wavenumber)
The solution provides detailed explanations in a 2-page Word document for the problem of plane wave propagation in electromagnetic field.