The pleasure of hiking in the world's highest mountains cannot be exaggerated. Neither can the hazard. Altitude sickness can occur in some people at altitudes as low as 2400 m, but serious symptoms do not usually occur until over 3600 m. Even then, it is not the height that is important, but rather the speed in which a person ascends to that altitude. Table 1 shows the pressure changes that occur as one ascends a mountain.Table 1 Pressure at various altitudesAir at sea level is about 21% oxygen and 78% nitrogen. The barometric pressure is around 760 mmHg. As altitude increases, the composition of air remains the same, but the number of oxygen molecules per breath is reduced. At 3600 meters, the barometric pressure is only about 480 mmHg, so the body takes in only about 60% of the oxygen per inhalation that it does at sea level. As a result, the body compensates for having less oxygen. Air pressure (Pa) above sea level is calculated using Equation 1:Equation 1:  P = 101325 (1 - 2.25577 x 10-5 h) 5.25where h = altitude above sea level in meters. In addition, high altitude and low air pressure cause fluid to leak from the capillaries in both the lungs and the brain, which can lead to fluid buildup. Continuing on to higher altitude without proper acclimatization can lead to potentially serious, even life-threatening altitude sickness.Acetazolamide is the most tried and tested drug for altitude sickness prevention and treatment. Unlike other treatments, this drug does not mask the symptoms but rather treats the problem. It works by increasing the amount of alkali (bicarbonate) excreted in the urine, making the blood more acidic. Acidifying the blood drives ventilation, which is the basis of acclimatization.Question 1What is the approximate partial pressure of oxygen at 1500 m? A.0.11 atmB.0.18 atmC.0.67 atmD.0.85 atm