Sodium, chloride or table salt is an example of a substance because

Table salt has a uniform and definite composition. It is not a mixture because the sodium and the chlorine are chemically bonded, meaning you cannot take the sodium out of the chlorine or vice versa.

Explanation:

All samples of salt are chemically identical, whereas a mixture can vary. For example, salt water is a mixture because you can have differing amounts of salt or water. The composition is not the same all the way throughout.

metals are good conductor of electricity. it has free electrons on their surface. according to electron pool theory, each atom present in a metal crystal losses all of its valence electron and as a result a pool of free is form. these pool of electrons are free to move and   conduct electricity easily   while making metal as good conductor.

the correct answer is a. the ability of electrons to flow throughout the metal.

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