Why is the entropy of any pure and perfectly crystalline substance at 0 K temperature zero?

For pure crystalline substance :

At what temperature entropy of a perfect crystalline substance is taken as zero?

Why are crystalline substances anisotropic?

This question has Statement I and Statement II. Of the four choices given after the Statements, choose the one that best describes the two Statements. Statement-I : Enthalpy and entropy of any elementary substance in the standard states are taken as zero. Statement-II : At absolute zero, particles of the perfectly crystalline substance become completely motionless.

Which law states entropy of all pure crystalline solids is zero at absolute zero ?

Why does the conductivity of a pure semiconductor increases with rise in temperature ?

Why does the concentration of OH^(-) ions in pure water increase with rise in temperature ? Does this increase make pure water alkaline ? Explain.

Give an example of volume expansion of a liquid on heating. The area of a solid substance at a temperature of T_1K is A_1 sq m and that at a temperature of T_2K is A_2 sq m.Write down the mathematical expression for the coefficient of area expansion-with unit, of that solid substance.

Which of the following statement(s) must be true for the entropy of a pure solid to be zero ? I. The temperature must be zero kelvin II. The solid must be perfectly crystalline Ill. The solid must be an element IV. The solid must be ionic