As part of a course on diffusion, you are to measure the diffusion coefficient of ammonia in $25C$ air, using the two$-$bulb capillary apparatus shown in Fig. $3\mathrm{.}1-2.$ In your apparatus, the bulbs have volumes of about $17c{m}^3,$ and the capillary is $2\mathrm{.}6cm$ long and $0\mathrm{.}083cm$ in diameter. You are told that you should make your measurements when the concentration difference is about half the initial value. $($a$)$ Use the ChapmanEnskog theory to estimate how long you should run your experiment. Answer: $3\mathrm{.}6hrs($b$)$ Why are you told to make your measurement near this particular concentration difference?

Please provide detailed answrr with reasoning.