Ahard, crystalline solid with a high melting point does not conduct electricity in any phase. this solid is most likely
(a) an ionic solid.
(b) a metallic solid.
(c) a molecular solid.
(d) a network covalent solid.

d. a network covalent solid.

Explanation:

A network covalent solid -

In these type of solids , the atoms are connected to each other via covalent bonds , its consists of large number of atoms connected in a three dimensional arrangement.

Hence, from the given information of the question,

The correct term from the given options is d. a network covalent solid.