In metallic colids, the forces of attraction are between the mobile valence electrons and

Analyze the question: It asks what the mobile (delocalised) valence electrons in a metal are attracted to. This is about metallic bonding.

Explain the concept: In a metal, atoms lose their outer (valence) electrons. These electrons become delocalised and form a "sea of electrons" that moves freely throughout the structure. What remains are positive metal ions (the nucleus plus inner electrons), arranged in a regular lattice. The metallic bond is the electrostatic attraction between the positive ions/nuclei and the sea of mobile electrons.

Evaluate each option:

• A. Atoms: Atoms are neutral overall, so they can't attract electrons electrostatically. In a metal, the valence electrons have left the individual atoms, so this is not correct.
• B. Neutrons: Neutrons have no charge, so there is no electrostatic attraction. Wrong.
• C. The negative ions: Metals do not contain negative ions in their lattice, and negative charges would repel the electrons. Wrong.
• D. Positively charged nuclei: The positive kernels (nuclei with their inner electrons) attract the negative mobile electrons. This is correct.

Answer: The forces of attraction in metallic solids are between the mobile valence electrons and the positively charged nuclei (positive metal ions).

Exam tip: Remember "positive ions in a sea of electrons". Any option mentioning negative ions or neutrons is a distractor for metallic bonding. Opposite charges attract, so the electrons must be attracted to something positive.