Q.State the third law of Thermodynamics.

The Third Law of Thermodynamics states that the entropy of a perfect crystal of a pure substance is exactly zero at 0 K.

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

At 0 K, a perfectly ordered crystalline substance has only one possible microstate (all its constituent particles are in their lowest possible, perfectly ordered arrangement), and since entropy is a measure of disorder/the number of accessible microstates, this unique, perfectly ordered state has zero entropy. This law is significant because it provides an absolute reference point from which the en …