Question

Why is glass transparent and brittle while copper is opaque and ductile

Answer 1

It is because copper is a metal and has free electrons but glass has not.

Answer 2

a material like copper is known as ductile - that is, it will flow,and can be drawnout into a wire without fracture. materiala such as glass that can be extended but do not show plastic deformation and will easily fracture are known as brittle materials.