The number of mole of oxygen in one litre of air containing 21% oxygen by volume, under standard condition is :

• (A). 0.0093 mole
• (B). 2.10 mole
• (C). 0.186 mole
• (D). 0.21 mole

To find the number of moles of oxygen in one liter of air containing 21% oxygen by volume, we can use the ideal gas law and the concept of molar volume at standard conditions.

Calculating Moles of Oxygen

At standard temperature and pressure (STP), one mole of any gas occupies approximately 22.4 liters. Given that air contains 21% oxygen, we can calculate the moles of oxygen in one liter of air as follows:

• Volume of oxygen in 1 liter of air = 21% of 1 liter = 0.21 liters
• Moles of oxygen = Volume of oxygen / Molar volume at STP
• Moles of oxygen = 0.21 liters / 22.4 liters/mole

Now, performing the calculation:

Moles of oxygen = 0.21 / 22.4 ≈ 0.0093 moles

Final Answer

Thus, the number of moles of oxygen in one liter of air is approximately 0.0093 moles. Therefore, the correct option is (A).