The number of moles of nitrogen present in one litre of air containing 15% nitrogen by volume, under standard condition, is:

Explanation

To find the number of moles of nitrogen present in one liter of air containing 15% nitrogen by volume under standard conditions, we can follow these steps:

### Step-by-Step Solution:

1. **Determine the Volume of Nitrogen:**
Since the air contains 15% nitrogen by volume, we can calculate the volume of nitrogen in 1 liter of air.
\[ \text{Volume of Nitrogen} = 15\% \text{ of 1 L} = \frac{15}{100} \times 1 \text{ L} = 0.15 \text{ L} \]

2. **Use the Ideal Gas Law:**
Under standard conditions (STP), 1 mole of an ideal gas occupies 22.4 liters. We can use this information to find the number of moles of nitrogen in the calculated volume.
\[ \text{Number of moles of Nitrogen} = \frac{\text{Volume of Nitrogen}}{\text{Volume occupied by 1 mole at STP}} = \frac{0.15 \text{ L}}{22.4 \text{ L/mole}} \]

3. **Calculate the Number of Moles:**
Now, we perform the calculation:
\[ \text{Number of moles of Nitrogen} = \frac{0.15}{22.4} \approx 0.0066964 \text{ moles} \]

4. **Express in Scientific Notation:**
To express this in scientific notation:
\[ 0.0066964 \text{ moles} \approx 6.69 \times 10^{-3} \text{ moles} \]

### Final Answer:
The number of moles of nitrogen present in one liter of air containing 15% nitrogen by volume under standard conditions is approximately \( 6.69 \times 10^{-3} \) moles.

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