How to determine which molecule has the highest melting point?

[gsingh2011]

The question is: Which substance has the highest melting point?
(A) CO (B) CO₂ (C) SiO₂ (D) P₂O₅

The answer is C but I don't know why (you obviously can't look up the values). I need to be able to figure these types of questions out regardless of the molecules given in the choices.

 

[Borek]

For the record: thread title doesn't make sense. Molecules don't have melting points. Substances do.

I am not aware of a bullet proof method for determining melting points. However, first two substances are gases at STP, so they are ruled out, and we are left with P₂O₅ and SiO₂. The latter is just a sand, and sand is pretty difficult to melt, so even not knowing anything about P₂O₅ I would say that's the answer.