The metallic bond in magnesium is stronger than that in calcium because magnesium has a

Analyze the question: We are comparing the strength of metallic bonding in magnesium (Mg) and calcium (Ca). Both are Group 2 elements, so each has 2 valence electrons.

Concept: Metallic bond strength depends on:

1. The number of delocalised (valence) electrons contributed per atom.
2. The charge on the metal cation.
3. The size of the atom or ion. A smaller size means a higher charge density, so the positive nuclei attract the "sea" of delocalised electrons more strongly.

Solution:

• Mg and Ca are both in Group 2, so each has 2 valence electrons. This rules out option C, because the number of valence electrons is the same.
• Mg (atomic number 12, 2,8,2) has 3 electron shells. Ca (atomic number 20, 2,8,8,2) has 4 shells.
• So Mg has a smaller atomic (and ionic) radius than Ca.
• With a smaller radius, the Mg²⁺ ions sit closer to the delocalised electrons. The attraction is stronger, so the metallic bond is stronger.
• Option A is the opposite of the true situation, since Mg is smaller, not larger.
• Option D is wrong because a lower melting point means a weaker metallic bond. Mg actually has a slightly higher melting point (about 650 °C) than... in fact Ca melts at about 842 °C, so Mg's melting point is not the reason, and "lower melting point" would not explain a stronger bond anyway.

Note on the data: Ca has a higher melting point than Mg in real data, which is an exception to the simple trend. However, the question asks for the reason based on the standard WASSCE explanation, which is atomic size. Among the options given, only B fits the reasoning.

Correct answer: B. Smaller atomic size

Tip: For metals in the same group, remember "smaller size, stronger bond." For metals in the same period, remember "more valence electrons, stronger bond" (for example, Al is stronger than Mg, which is stronger than Na).