How many atoms are present in 6.0 g of magnesium? [Mg = 24, N_A = 6.02 × 10²³ mol⁻¹]

Correct answer: 1.51 × 10²³ (Option C)

Explanation:

• Number of moles of Mg = mass ÷ molar mass = 6.0 g ÷ 24 g mol⁻¹ = 0.25 mol.
• Number of atoms = moles × Avogadro’s constant = 0.25 × 6.02 × 10²³ = 1.505 × 10²³ ≈ 1.51 × 10²³.

Why the others are incorrect:

• 1.20 × 10²² and 2.41 × 10²²: far too small; they come from arithmetic or unit mistakes.
• 3.02 × 10²³: corresponds to 0.5 mol (e.g., 12 g of Mg), not the 0.25 mol present here.