12930. When α is absorptivity, ρ is reflectivity and τ is transmittivity, then for a diathermanous body, September 13, 2025 by Admin α = 1, ρ = 0 and τ = 0 α = 0, ρ = 1 and τ = 0 α = 0, ρ = 0 and τ = 1 α + ρ = 1 and τ = 0 ✅ The correct answer is option D.