Why crystalline solids have a sharp melting point?

Why metallic solids are opaque?

Why alpha - amino acids have relatively higher melting point than corresponding haloacids ?

Why do solids have definite shapes ?

Statement : Due to Frenkel defect the density of the crystalline solid remains same. Explanation : In Frenkel defect, no cations or anions leave the lattice.

The transition elements have high melting points.