Which of the following is expected to have zero entropy?

Question

I. N2(g) at 273 K

II. SiO2 (s, amorphous) at 0 K

III. NaCl(s) perfectly ordered crystal at 25 K

IV. NaCl(s) perfectly ordered crystal at 0 K

Answer 1

IV is the correct answer. This is expected from the third law of thermodynamics which states that the entropy of a perfect crystal at absolute zero approaches zero.