The relative thermal conductivity of common soil constituents (quartz, water, and air) is approximately in the ratio of 333 : 23 : 1.

• 333 : 23 : 1: Thermal conductivities are roughly 8.8 W/m·K for quartz, 0.6 W/m·K for water, and 0.026 W/m·K for air, which gives a relative ratio of approximately 333 : 23 : 1.
• 333 : 43 : 3: An incorrect ratio with distorted values for water and air.
• 333 : 33 : 1: An incorrect proportion often cited erroneously in unverified texts.
• 333 : 23 : 3: Incorrect baseline value assigned to the gaseous phase.

• In soil physics, gas exchange through soil aeration occurs predominantly via molecular diffusion governed by Fick's first law: J = -D * (dc/dx).
• The relative diffusion coefficient (D/D0, where D is apparent diffusivity in soil and D0 is diffusivity in free air) depends directly on the air-filled porosity (S) of the soil.
• In natural soils, real D/D0 values typically range between 0.005 and 0.20; H.L. Penman (1940) formulated the classical empirical equation D/D0 = 0.66 * S, where 0.66 is an empirical tortuosity coefficient.
• RPSC officially keyed Option 4 (0.66) based on Penman's constant in the soil diffusion equation.