Explanation: The skin effect describes the phenomenon where alternating current (AC), particularly at radio frequencies (RF), flows predominantly through the outer surface of a conductor rather than uniformly throughout its cross-section. This occurs because the changing magnetic fields created by the AC current induce opposing eddy currents within the conductor itself, effectively pushing the main current towards the surface. Crucially, this effect *becomes more pronounced as the frequency increases*. At higher RF frequencies, the current is confined to a much thinner layer closer to the conductor's surface, reducing the effective cross-sectional area available for current flow and increasing the conductor's resistance. Option B is incorrect because the skin effect *diminishes* as frequency decreases, allowing current to distribute more evenly. Options C and D are incorrect because the skin effect is an electromagnetic phenomenon related to current distribution, not primarily a thermal effect that directly increases or decreases impedance, although it does increase effective resistance at RF.