Compare total atoms using moles and atoms per formula unit

Steps:

• Identify atoms per formula unit: H₂O (3), CO₂ (3), CH₄ (5), HCl (2).
• Calculate total formula units: multiply moles by Avogadro's constant (same for all, so compare moles × atoms per unit).
• Compute for each: A (0.5 × 3 = 1.5), B (1 × 3 = 3), C (1 × 5 = 5), D (2 × 2 = 4) in units of moles of atoms.
• Select highest: 5 from C.

Why C is correct:

• CH₄ has 5 atoms per molecule (1 C + 4 H), so 1.0 mol yields 5 mol atoms, per Avogadro's number definition.

Why the others are wrong:

• A: 0.5 mol H₂O gives 1.5 mol atoms (3 per molecule).
• B: 1.0 mol CO₂ gives 3 mol atoms (3 per molecule).
• D: 2.0 mol HCl gives 4 mol atoms (2 per molecule).

Final answer: C