Which of the following would weigh the least? (Atomic masses C=12, O=16, Na=23)

6.023 x 10²² atoms of carbon

Reason — To determine which of the options weighs the least, let's calculate the mass of each:

1. 2 gram atoms of oxygen:
   • A gram atom of oxygen refers to 1 mole of oxygen atoms, which has a mass of its atomic mass in grams.
   • Oxygen has an atomic mass of 16 g/mol.
   • Therefore, 2 gram atoms of oxygen would weigh 2 x 16 g = 32 grams.
2. One mole of sodium:
   • The atomic mass of sodium is 23 g/mol.
   • Thus, one mole of sodium weighs 23 grams.
3. 22.4 litres of carbon dioxide at STP:
   • At Standard Temperature and Pressure (STP), 1 mole of any gas occupies 22.4 liters.
   • The molecular formula for carbon dioxide is CO₂.
   • The molar mass of CO₂ is 12 (for C) + 2 x 16 (for O) = 44 grams/mol.
   • Therefore, 22.4 litres of carbon dioxide weighs 44 grams.
4. 6.023 x 10²² atoms of carbon:
   • Avogadro's number is 6.023 x 10²³, which is the number of atoms in 1 mole.
   • Therefore, 6.023 x 10²² atoms of carbon is $\frac{1}{10}$ of a mole of carbon.
   • The atomic mass of carbon is 12 g/mol.
   • Therefore, $\frac{1}{10}$ mole of carbon has a mass of $\frac{12}{10}$ = 1.2 grams.

Comparing the masses:

1. 2 gram atoms of oxygen = 32 grams
2. One mole of sodium = 23 grams
3. 22.4 litres of carbon dioxide at STP = 44 grams
4. 6.023 x 10²² atoms of carbon = 1.2 grams

Hence, out of the given options, 6.023 x 10²² atoms of carbon will weigh the least.