According to the third law of thermodynamics, what is the entropy of a perfect crystal at absolute zero?

The third law of thermodynamics states that as the temperature of a perfect crystal approaches absolute zero, the entropy approaches a constant minimum value. For a perfect crystal, this minimum value is defined to be zero. This is because a perfect crystal at zero Kelvin has a perfectly ordered state, with all its constituent particles occupying a single, specific arrangement.

In a perfect crystal, there are no microstates or configurations available that would contribute to disorder, which is what entropy measures. Therefore, at absolute zero, the lack of thermal motion and the uniform arrangement result in zero entropy. This is a fundamental principle that helps establish a reference point for measuring entropy in other systems, making the correct answer zero entropy.

The incorrect options can be outlined as follows: maximum entropy implies a state of complete disorder, which does not apply to a perfect crystal at absolute zero. Infinite entropy would suggest an unbounded level of disorder, which is also contrary to the ordered nature of a perfect crystal. Undefined entropy implies a lack of clarity regarding the state of the system, which is not the case here since the conditions of a perfect crystal at absolute zero are well-defined and understood.