Question

Suppose an unknown substance has a melting temperature of 1,200 degrees Celsius and a density of 16.7 g/cm3. However, the different individual atoms that make up the element have very different melting temperatures and densities. The unknown substance is most likely a what?

Answer 1

An odd question. Macroscopic concepts such as melting temp, density, cannot be applied to microscopic particles such as atoms.

An atom does not have a melting temperature.

I am wondering if you mistyped the word element here, and should have used instead substance.

Compound may be what you are looking for.

Answer 2

Alloy

Answer 3

compound