The metallic bonding in aluminium is strong because of large number of

Step 1: Analyze the question The question asks why metallic bonding in aluminium is strong, and which kind of electrons there are a "large number" of.

Step 2: The concept Metallic bonding is the electrostatic attraction between positive metal ions (cations) and a "sea" of electrons that are free to move throughout the structure. The strength of the bond depends on:

• the charge on the metal ion (higher charge means stronger attraction),
• the number of electrons released into the sea,
• the size of the ion (smaller ions mean stronger attraction).

Step 3: Apply it to aluminium

• Aluminium (Group 3, electron configuration 2,8,3) has 3 valence electrons.
• Each atom gives up all 3 to the shared pool, forming Al³⁺ ions.
• This produces a large number of delocalized electrons, so the attraction between Al³⁺ ions and the electron sea is strong. That is why aluminium has a higher melting point than sodium (1 delocalized electron per atom) or magnesium (2 per atom).

Step 4: Evaluate the options

• A. Delocalized electrons: Correct. These are the mobile electrons that hold the cations together in the metallic bond.
• B. Immobile electrons: Wrong. Metallic bonding depends on mobile electrons, not fixed ones.
• C. Lone pair electrons: Wrong. Lone pairs belong to covalent molecules such as NH₃ and H₂O.
• D. Valence electrons: This is a tempting option because valence electrons are the source of the electron sea. But valence electrons exist in every atom, including non-metals, and they are not what specifically holds a metal together. It is the fact that they become delocalized that creates metallic bonding.

Answer: A. delocalized electrons

Exam tip: Remember "metallic bond = cations + sea of delocalized electrons." When a question asks about the strength of a metallic bond, think of the number of delocalized electrons and the charge on the ion. Al³⁺ has more of both than Na⁺ or Mg²⁺.