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GATE 2025 Chemical Engineering, Q34 · Mechanical Operations

The correct answer is 95 to 97.

Question

Oil is extracted from mustard seeds having 20 wt% oil and 80 wt% solids, using hexane as a solvent. After extraction, the hexane-free residual cake contains 1 wt% oil. Assuming negligible dissolution of cake in hexane, the percentage oil recovery in hexane is ____% (rounded off to the nearest integer).

Official answer: 95 to 97

Why

GATE 2025 official key: 95 to 97%. Basis 100 kg seed: 80 kg solids, 20 kg oil. Residual cake oil = 1 wt% of cake, so oil left =(1/99)×80≈0.808= (1/99) \times 80 \approx 0.808 kg. Recovery =(20−0.808)/20≈= (20−0.808)/20 \approx 96%.

Explanation cross-checked for consistency. Final answer matches the official IIT answer key.

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