A certain substance contained atoms whose outer electrons were freely moving between the nuclei. This substance most likely contains _____ bonds.

The question describes a substance where outer electrons are "freely moving between the nuclei." This characteristic is unique to metallic bonding.

• Metallic bonds involve a "sea" of delocalized valence electrons that are not associated with any single atom but are shared among all the metal atoms in the structure. These electrons are free to move throughout the entire metallic lattice.
• Ionic bonds involve the transfer of electrons, forming fixed positive and negative ions.
• Covalent bonds involve the sharing of electron pairs between specific atoms, localizing the electrons between those two atoms.
• Coordinate bonds are a type of covalent bond where one atom donates both electrons to the shared pair, but the electrons are still localized between the bonded atoms.

Therefore, the substance most likely contains metallic bonds.

The correct option is D.
The substance most likely contains D. metallic bonds.