849. For infinite parallel planes having emis-sivities ε₁ & ε₂, the interchange factor for radiation from surface 1 to surface 2 is given by September 6, 2025 by Admin A. (ε₁ + ε₂)/ε₁.ε₂ B. Ε₁.ε₂/(ε₁ + ε₂ – ε₁.ε₂) C. Ε₁.ε₂ D. Ε₁ + ε₂ ✅ The correct answer is option B.