Final answer:
The molecular mass of water (H2O) is 18 g/mol, resulting from the sum of the masses of two hydrogen atoms and one oxygen atom. Regardless of sample size, the mass ratio of hydrogen to oxygen in a water molecule remains constant. Option 2 is correct.
Step-by-step explanation:
The molecular mass of water (H2O) is calculated by adding the atomic masses of its constituent atoms. Water has two hydrogen atoms and one oxygen atom. The atomic mass of hydrogen is approximately 1 g/mol and for oxygen, it is approximately 16 g/mol. Hence, the molecular mass of water is:
(2 × Atomic mass of H) + (1 × Atomic mass of O)
(2 × 1 g/mol) + (1 × 16 g/mol)
2 g/mol + 16 g/mol = 18 g/mol
Therefore, the correct answer is option 2: 18.
The mass ratio of hydrogen to oxygen in a molecule of water is 2:16, but this ratio is representative of the atomic masses and does not change with the size of the sample. Whether the sample is 10 L or 10,000 L, the mass ratio of hydrogen to oxygen remains the same, because a molecule of water invariably contains 2 hydrogen atoms and 1 oxygen atom.