Answer:
2.11 x 10²⁴ molecules.
Explanation:
Using cross multiplication:
1.0 mole of H₂O contains → 6.022 x 10²³ molecules.
3.5 mole of H₂O contains → ??? molecules.
∴ 3.5 mole of H₂O contain = (3.5 mol)(6.022 x 10²³) = 2.11 x 10²⁴ molecules.