A window used to thermally insulate a room from outside consists of two parallel glass sheets each of area \(2.6 \mathrm{~m}^2\) and thickness \(1 \mathrm{~cm}\) separated by \(5 \mathrm{~cm}\) thick stagnant air. In the steady state, the room glass interface is at \(18^{\circ} \mathrm{C}\) and the glass-outdoor interface is at \(-2{ }^{\circ} \mathrm{C}\). If the thermal conductivities of glass and air are respectively \(0.8 \mathrm{Wm}^{-1} \mathrm{~K}^{-1}\) and \(0.08 \mathrm{Wm}^{-1} \mathrm{~K}^{-1}\), the rate of flow of heat through the window is

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.