Number of atoms in 1 mol of water.

**The reasoning** One mole of water (H₂O) contains Avogadro's number of *molecules* = 6.02 × 10²³ molecules. But the question asks for *atoms*, not molecules! Each water molecule has **3 atoms total**: 2 hydrogen atoms + 1 oxygen atom. So: Total atoms = 6.02 × 10²³ molecules × 3 atoms/molecule = **3 × 6.02 × 10²³ atoms** This is the principle of **molecular composition** meeting Avogadro's number. Always check whether they're asking for molecules or atoms! **Why the wrong options tempt you** **A** tricks you if you forget water is H₂O and just think "1 mole = 6.02 × 10²³" without counting atoms per molecule. **B** is what you'd get if you calculated it out (1.806 × 10²⁴), but they want the answer in factored form. **D** is completely wrong—probably confusing atomic mass concepts with atom counting. **Quick takeaway** One mole gives you 6.02 × 10²³ *molecules*; multiply by the number of atoms *per molecule* to get total atoms—for H₂O, that's always ×3!