Final answer:
The question on phase velocity in a material at a given skin-depth and frequency cannot be answered without further information on the material's properties such as permittivity and permeability.
Step-by-step explanation:
The student is asking about the propagation speed of an electromagnetic wave in a conductor, given the skin-depth at a specific frequency. The skin-depth δ, at a frequency f, is given by the equation δ = √(2/ρπμf), where ρ is the resistivity, μ is the permeability, and f is the frequency. To find the propagation velocity, typically the phase velocity, one would need to know the material's permeability and permittivity, as it relates to the general formula v_p = 1/√(με). However, this problem has not given sufficient information to directly calculate the phase velocity. Typically, though, the propagation speed of an electromagnetic wave in a good conductor is much less than the speed of light due to the interaction with the free electrons in the conductor. The actual value would require additional values that are not provided in the question.