Concept:The formal IUPAC definition of a "mole" relies on a physical baseline standard that perfectly mirrors Avogadro's constant.
Formula:$$ 1 \text{ mole} \equiv \text{Atoms in 12.000g of } ^{12}\text{C} $$
Solution:- In the International System of Units (SI), the mole was historically defined precisely as the amount of substance that contains as many elementary entities (e.g., atoms, molecules, ions) as there are atoms in exactly 12 grams of the Carbon-12 isotope.
- This specific mass (12g) of this specific isotope (C-12) contains exactly \( 6.022 \times 10^{23} \) atoms, which mathematically calibrates the entire concept of the mole.
Why other options are incorrect:- 1.008g of hydrogen gas: \( \text{H}_2 \) gas has a molar mass of ~2.016 g. 1.008g is only a half-mole of hydrogen molecules, failing the definition.
- 16 g of oxygen gas: \( \text{O}_2 \) has a molar mass of 32. 16g is only half a mole.
- 12 g of magnesium: Mg has a molar mass of ~24. 12g is a half-mole.
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