Extend: How could scientists use this physical property to identify an unknown substance? Please explain by using gold as an example and showing how the math would be calculated.

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elements make up everything, and they combine to make compounds.

the answer is c

ca has a crystalline lattice with positive ions (since it is a metal, metals are positively charged) and electrons flow freely in its structure since the ca atoms have a large nuclear radius so the electrons are not tightly held, therefore the electrons can flow freely since they are not being highly attracted by the nucleus. moreover, one of the properties of metals are that they are conductors of electricity, thus proving ca is the element.