Question

why are metals good conductors of electricity whereas class is a bad conductor of electricity give reason

Answer 1

Metals have free electrons which helps them in the conduction of electricity whereas non metals have no free electrons which makes them a poor conductor of electricity. However some exceptions are there.
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Answer 2

Metal has a ability to loose it's electron to form stability and due to this, charges are formed and these charge carrier conducts electricity. Hence metal is a good conductor of electricity.