Oxygen diffuses from the surface of insects to the interior through tiny tubes called tracheae. An average trachea is about 2 mm long and has cross-sectional area of 2 × 10-9 m2. Assuming the concentration of oxygen inside is half what it is outside in the atmosphere,

(a) Show that the concentration of oxygen in the air (assume 21% is oxygen) at 20°C is about 8.7 mol / m3, then

(b) Calculate the diffusion rate J, and

(c) Estimate the average time for a molecule to diffuse in. Assume the diffusion constant is 1 × 10-5 m2 / s.