"Diamond is an extremely bad conductor of electricity. " Why?

Bad conductor of electricity is

Poor conductor of electricity is

What is meant by bad conductors of electricity?

Which among these is bad conductor of electricity?

What is meant by good conductors of electricity?

Which among these is good conductor of electricity?

Why ionic compounds are bad conductors of electricity in crystalline state but good conductors of electricity in aqueous solutions ?

Solid NaCl is a bad conductor of electricity because

Which metal is the best conductor of electricity?