In descending order of magnitude, the thermal conductivity of $$(a)$$ Pure iron, $$(b)$$ liquid water, $$(c)$$ saturated water vapour, and $$(d)$$ aluminum can be arranged as

For a given heat flow and for the same thickness, the temp drop across the material will be maximum for

Two insulting materials of thermal conductivity $$K$$ and $$2K$$ are available for lagging a pipe carrying a hot fluid. If the radial thickness of each material is same

Thermal conductivity is lower for