Covalent bonds never conduct electricity well.
Answer: Option D
Step-by-step explanation:
For a metal or conductor to conduct electricity, there must be free electrons moving freely on the outermost orbit so that when there is a potential difference, the electrons flows and produce electricity by theory motion.
Hence the outermost shell must be unstable for a conductor, else there will be no free electrons. In covalent bonds, electrons are shared which makes them difficult to move and produce electricity.