1. a) Is air a pure substance or mixture? (0.5 pt)

b) List the top three major components of air and their respective percent composition. (1 pt)

2. a) What is air pressure in pounds per square inch (psi) at sea level? (0.5 pt)

b) How much force in pounds will be exerted by air on a typical office desk top that measures 45 in x 24 in? show work and proper units for full credit ( 2 pt)

3. How does air pressure change with altitude? Why? (2 pt)
4. Breathing involves changing pressure inside our lungs,

a) During inhalation, fresh air moves into lungs, how does it work? (2 pt)

b) During exhalation, waste air moves out of lungs, how does it work? (2 pt)