Question

why only on metal free electrons are present​

Answer 1

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WHEN ELECTRICITY FLOWS, THE ELECTRONS ARE CONSIDERED "FREE" ONLY BECAUSE

THERE ARE MORE ELECTRONS THAN THERE SHOULD BE, AND BECAUSE THE TRANSITION METALS, SUCH AS IRON, COPPER, LEAD, ZINC, ALUMINIUM, GOLD ETC. ARE WILLING TO TRANSIENTLY ACCEPT AND GIVE UP ELECTRONS FROM THE D- ORBITALS OF THEIR VALENCE SHELL.

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