Concept:Metallic bonding is the force of attraction between free-moving valence electrons and fixed positive metal ions.
Explanation:In a metallic solid, metal atoms release their valence electrons.
These electrons move freely through the whole structure, forming a “sea of electrons.”
Meanwhile, the remaining metal ions are positively charged.
The mobile valence electrons are attracted to these positively charged nuclei or ions.
This electrostatic attraction binds the metal atoms together in a regular lattice.
Answer:D. positively charged nuclei