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 substance have very different melting temperatures and densities. The unknown substance is most likely a compound, solution, or a molecule

Answer 1

atoms do not have melting temperatures, atoms do not melt.

I assume the problem writer meant elements made up of those differing atoms had differing melting points.

Compound.