Answer the following with reference to the second law of thermodynamics.
(i) State the mathematical condition that must be satisfied by the total entropy change of the universe for any process.
(ii) Distinguish, on the basis of the sign of the total entropy change, between a reversible process, a spontaneous (irreversible) process and an impossible process.
(iii) A drop of perfume released at one corner of a closed, still room eventually spreads uniformly throughout the room without any external aid. Explain this observation in the light of your answer to part (i).