A slab of stone of area \(3600 \mathrm{~cm}^2\) and thickness \(10 \mathrm{~cm}\) is exposed on the lower surface to steam at \(100^{\circ} \mathrm{C}\). A block of ice at \(0^{\circ} \mathrm{C}\) rests on upper surface of the slab. In one how \(4.8 \mathrm{~kg}\) of ice is melted. The thermal conductivity of the stone in \(\int \mathrm{s}^{-1} \mathrm{~m}^{-1} \mathrm{k}^{-1}\) is (Latent heat of ice \(=3.36 \times 10^5 \mathrm{~J} / \mathrm{kg}\) )

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.