Concept:The number of atoms in a pure elemental sample is directly proportional to its number of moles. Therefore, whichever sample has the highest mole count will contain the most atoms.
Formula:$$ \text{Moles} = \frac{\text{Mass}}{\text{Atomic Mass}} $$
Solution:- Option A (Mg): Atomic mass = 24. \( \text{Moles} = 7 / 24 \approx 0.29 \text{ mol} \).
- Option B (Na): Atomic mass = 23. \( \text{Moles} = 8 / 23 \approx 0.35 \text{ mol} \).
- Option C (Al): Atomic mass = 27. \( \text{Moles} = 9 / 27 = 0.33 \text{ mol} \).
- Comparing the calculated moles: 0.35 mol (Sodium) > 0.33 mol (Aluminum) > 0.29 mol (Magnesium).
- Since Sodium possesses the highest number of moles, it inherently contains the highest number of discrete atoms.
Why other options are incorrect:- 7g Mg and 9g Al: While Aluminum has the highest raw mass (9g), its heavier atomic nucleus means fewer actual atoms are present compared to 8g of lighter Sodium.
- All same: Impossible, since mass/atomic-mass ratios do not mathematically equate here.
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