Yield strength in steels is controlled mainly by how much carbon gets locked into the iron lattice. Copper alloys are soft non-ferrous metals and naturally sit at the bottom of this comparison. Among the three steels, more dissolved carbon means more hard cementite forms as the steel cools, and this cementite blocks dislocations from sliding, which is exactly what raises the resistance to plastic flow. Moving from mild steel to medium carbon steel to high carbon steel, the carbon content keeps rising, so the yield strength keeps rising too. Since high-carbon steel carries the most carbon among the given choices, it gives the maximum yield strength.