Concept:Metallic bond strength increases when the metal ions are smaller, because the attraction between the positive ions and delocalised electrons becomes stronger.
Explanation:Both magnesium and calcium are in Group 2, so each atom releases two valence electrons into the metallic bond.
Moving down the group from magnesium to calcium, atomic size increases because additional electron shells are added.
In calcium, the larger atomic radius means the nucleus is farther away from the delocalised electrons, so the metallic attraction is weaker.
In magnesium, the smaller atomic size allows its nucleus to pull the delocalised electrons more strongly.
Hence, the metallic bond in magnesium is stronger, giving magnesium a higher melting point than calcium.
Answer:Magnesium has a stronger metallic bond than calcium because magnesium has a
smaller atomic size (Option B).