Question

Why do human beings have difficulty breathing at high elevation ?

• A. $O_2$ makes up lower percentage of air there
• B. the temperature is lower there
• C. The barometric pressure is higher there
• D. $P{O}_2$ is lower there

Answer 1

The correct option is D $P{O}_2$ is lower there

Human beings have difficulty breathing at high elevation because high-altitude atmospheric pressure decreases exponentially with altitude while the $O_2$ fraction remains constant to about $100$ km, So ${PO}_2$ decreases exponentially with altitude as well.