Final answer:
The Lewis electron-dot diagram that represents a substance that does not have a covalent bond is D. He, since helium has a full valence shell and does not form stable covalent bonds.
Step-by-step explanation:
The Lewis electron-dot diagram which represents a substance that does not have a covalent bond is D. He. Helium (He) is a noble gas with a full valence shell, typically having two electrons. This noble gas does not form stable covalent bonds because it already satisfies the octet rule (or, in the case of helium, the 'duet' rule) with its full valence shell. In contrast, substances like H2 and O2 are diatomic molecules with covalent bonds between the atoms.
NaCl consists of ionic bonds between Na+ and Cl−. The molecular orbital energy diagram predicts that a He2 molecule would not be stable because it would have equal numbers of bonding and antibonding electrons.