Q.State the Third law of Thermodynamics.

The Third Law of Thermodynamics states that the entropy of a perfectly crystalline substance is zero at absolute zero temperature (0 K).

Entropy is a measure of the disorder or randomness of a system. As temperature decreases, the thermal motion of particles decreases, and so does the disorder of the system. The Third Law of Thermodynamics states:

"The entropy of a perfectly ordered crystalline substance is taken as zero at the absolute zero of temperature (0 K)."

At 0 K, in a perfect crystal, every particle occupies a fixed, precisely ordered position in the lattice with no thermal motion at all, so there is only ONE possible microscopic arrangement (perfect order) — and since entropy is related to the number of possible microstates, this single-microstate condition corresponds to zero entropy.

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