Why does hexaphenylbenzene have a high melting point?

The melting point is a feature of inter-molecular forces of attraction between molecules of a substance

The bigger the size of a molecule more the van der waal forces between molecules and more the attraction and hence more the melting point and boiling point of any substance.

If we look at the structure of  hexaphenylbenzene we will be able to realize that it is a big molecule with a benzene ring having six more benzene ring (as shown in the diagram)

Thus it has high melting point

answer; /// the amount of material dissolved in a measure of liquid(concentration) the above statement is (true); /// good luck

the temperature of the gas, in k, not celsius.