18 g of water contain:

Options

A. 1 g atom of hydrogen
B. 2 g atoms of hydrogen
C. 3 g atoms of hydrogen
D. None of the above.

Answer

To solve the problem of how many gram atoms of hydrogen are present in 18 g of water (H₂O), we can follow these steps:

### Step 1: Determine the Molecular Weight of Water
The molecular formula of water is H₂O. To find the molecular weight, we need to sum the atomic weights of its constituent elements:
- Hydrogen (H) has an atomic weight of approximately 1 g/mol.
- Oxygen (O) has an atomic weight of approximately 16 g/mol.

Thus, the molecular weight of water (H₂O) is:
\[ \text{Molecular weight of H₂O} = (2 \times 1) + (1 \times 16) = 2 + 16 = 18 \text{ g/mol} \]

### Step 2: Calculate the Number of Moles of Water
Using the formula for calculating the number of moles:
\[ \text{Number of moles} = \frac{\text{Weight of substance}}{\text{Molecular weight of substance}} \]
We can substitute the values we have:
\[ \text{Number of moles of H₂O} = \frac{18 \text{ g}}{18 \text{ g/mol}} = 1 \text{ mole} \]

### Step 3: Determine the Number of Gram Atoms of Hydrogen
Each molecule of water (H₂O) contains 2 hydrogen atoms. Therefore, 1 mole of water contains:
\[ \text{Number of gram atoms of H} = 2 \times \text{Number of moles of H₂O} = 2 \times 1 = 2 \text{ gram atoms of hydrogen} \]

### Conclusion
Thus, 18 g of water contains **2 gram atoms of hydrogen**.

### Final Answer
The correct option is **2 gram atoms of hydrogen**.

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