True, the entropy of a perfectly ordered crystalline substance at 0 K is 0 J/mol.
The third law of thermodynamics states that, the entropy of a system approaches a constant value as the temperature of the system approaches absolute zero.
The entropy of any perfectly ordered, crystalline substance at absolute zero temperature is zero. That is, the entropy of a pure, perfect crystalline substance at 0 K is 0 J/K.
Thus, we can conclude that the given statement is true. The entropy of a perfectly ordered crystalline substance at 0 K is 0 J/mol.
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