\(M \mathrm{~kg}\) of water at \(t^{\circ} \mathrm{C}\) is divided into two parts so that one part of mass \(m \mathrm{~kg}\) when converted into ice at \(0^{\circ} \mathrm{C}\) would release enough heat to vapourise the other part, then \(\frac{m}{M}\) is equal to (Specific heat of water \(=1 \mathrm{cal} \mathrm{g}^{-1}{ }^{\circ} \mathrm{C}^{-1}\), Latent heat of fusion of ice \(=80 \mathrm{cal} \mathrm{g}^{-1}\), Latent heat of steam \(=540 \mathrm{cal} \mathrm{g}^{-1}\) )

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.