Question

which property do nonpolar covalent and polar covalent compounds demonstrate?
very high melting points
malleability
good electrical conductor
insulator

Explanation:

Nonpolar covalent and polar covalent compounds are made up of molecules. In these compounds, there are no free - moving electrons (as in metals which are good electrical conductors) or ions (as in ionic compounds which can conduct electricity in molten or aqueous state). Since there are no charge carriers available for the conduction of electricity, they are insulators.
High melting points are a characteristic of ionic and some network covalent compounds (due to strong ionic or covalent bonds). Malleability is a property of metals (due to the sea of electrons and the ability of metal ions to slide over each other).

Answer:

insulator