What substance has the highest melting and boiling point?
I think that carbon (graphite, and diamond) has the highest boiling point. In fact, it sublimes. IIRC, this happens at temperatures between 5000 and 6000 C. Maybe it is not the compound with the highest boiling point, but it certainly is among the compounds with the highest boiling point. Of course, all this must be specified at atmospheric pressure. At much higher pressure, such as in the core of the planet Jupiter, even hydrogen can exist in solid or liquid state, while white-hot, with metal-like properties. But that is at a pressure of millions of earth’s atmospheres.
