Why are crystalline substances anisotropic?

For pure crystalline substance :

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

Why amorphous solids are called isotropic whereas crystalline solids are called 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.

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

'Crystalline solids-are anisotropic in nature.' What does this statement mean?

A crystalline solid is anisotropic, whereas an amorphous solid is isotropic. Explain with reasons.

Assertion: Crystalline solids are anisotropic. Reason: Crystalline solids are not as closely packed as amorphous solids.

What are the crystalline and amorphous allotropic forms of carbon?