The number of moles of oxygen in 1 L of air containing `21%` oxygen by volume , under standard conditions , is

Options

A. 0.0093 mole
B. 2.10 moles
C. 0.186 mole
D. 21 mole

Answer

To find the number of moles of oxygen in 1 L of air containing 21% oxygen by volume under standard conditions, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Composition of Air**:
- The air contains 21% oxygen by volume. This means that in 1 liter of air, 21% of that volume is oxygen.

2. **Calculate the Volume of Oxygen**:
- To find the volume of oxygen in 1 liter of air:
\[ \text{Volume of Oxygen} = 21\% \text{ of } 1 \text{ L} = \frac{21}{100} \times 1 \text{ L} = 0.21 \text{ L} \]

3. **Use the Molar Volume at STP**:
- At Standard Temperature and Pressure (STP), the molar volume of a gas is 22.4 liters. This means that 1 mole of any gas occupies 22.4 liters.

4. **Calculate the Number of Moles of Oxygen**:
- To find the number of moles of oxygen in the calculated volume:
\[ \text{Number of Moles} = \frac{\text{Volume of Oxygen}}{\text{Molar Volume at STP}} = \frac{0.21 \text{ L}}{22.4 \text{ L/mol}} \]
- Performing the calculation:
\[ \text{Number of Moles} = \frac{0.21}{22.4} \approx 0.00938 \text{ moles} \]

5. **Final Answer**:
- Therefore, the number of moles of oxygen in 1 L of air containing 21% oxygen by volume under standard conditions is approximately **0.00938 moles**.