The number of water molecules in one litre of water is:

Options

A. 18
B. `18 xx 1000`
C. `6.022 xx 10^(23)`
D. `3.3 xx 10^(25)`

Explanation

To find the number of water molecules in one liter of water, we can follow these steps:

### Step-by-Step Solution:

1. **Convert Volume to Milliliters**:
- We know that 1 liter is equivalent to 1000 milliliters (ml).
- Therefore, the volume of water is:
\[ \text{Volume} = 1000 \, \text{ml} \]

2. **Determine the Density of Water**:
- The density of water is approximately 1 gram per milliliter (g/ml).
- This means that 1 ml of water has a mass of 1 gram.

3. **Calculate the Mass of Water**:
- Using the density formula (Density = Mass/Volume), we can find the mass of 1000 ml of water:
\[ \text{Mass} = \text{Density} \times \text{Volume} = 1 \, \text{g/ml} \times 1000 \, \text{ml} = 1000 \, \text{grams} \]

4. **Calculate the Moles of Water**:
- The molar mass of water (H₂O) is approximately 18 grams per mole.
- To find the number of moles, we use the formula:
\[ \text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}} = \frac{1000 \, \text{grams}}{18 \, \text{g/mol}} \approx 55.55 \, \text{moles} \]

5. **Calculate the Number of Molecules**:
- To find the number of molecules, we use Avogadro's number, which is approximately \(6.022 \times 10^{23}\) molecules per mole.
- The formula to calculate the number of molecules is:
\[ \text{Number of Molecules} = \text{Moles} \times \text{Avogadro's Number} \]
- Substituting the values we have:
\[ \text{Number of Molecules} = 55.55 \, \text{moles} \times 6.022 \times 10^{23} \, \text{molecules/mole} \approx 3.33 \times 10^{25} \, \text{molecules} \]

### Final Answer:
The number of water molecules in one liter of water is approximately:
\[ \text{Number of Molecules} \approx 3.33 \times 10^{25} \]

---