Keep your leg at a 90-degree angle and your knee and foot at the same height. Avoid rotating your spine at any point during the exercise. Pause at the top for two seconds before lowering your knee to the floor. Repeat 15-25 times before performing the exercises with the other leg.
Inhaled air is about 20-percent oxygen. Exhaled air is about 15-percent oxygen. Therefore, about 5-percent of breathed air is consumed in each breath. That air is converted to carbon dioxide. So, as far as how much air is actually used, human beings take in about 550 liters of pure oxygen per day. A person who is exercising uses a lot more oxygen than that.
(b) According to MadSci: The amount of air breathed by an average adult varies from 6 Litre/minute (when at rest) to 50 Litre/minute after hard exercise. So, at rest the amount of Oxygen absorbed by the blood in the lungs is 300 milliLitre/minute to 3,500 mL/minute. My Calculations for a person at rest: In 1 day the volume of O2 absorbed by a person at rest is 300mL/minute x 60 minute/hour x 24 h/day = 432,000 mL/day or 432 L/day. Since the mass of 1 mole of O2 is 32 gram and 1 mole of any gas has a volume of 22.4 L, the number of mole/day is 432 L/day / 22.4 L/mole = 19.28 mole.